Fortschritte der Chemie Organischer Naturstoffe / Progress in the Chemistry of Organic Natural Products / Progres dans la Chimie des Substances Organiques Naturelles

468 Pages·1954·12.96 MB·English

by  H. H. Inhoffen, H. Schmid, K. Brückner, R. B. Corey, K. Freudenberg, R. Lemberg, L. Pauling, S. Peat, W. A. Schroeder (auth.)

FORTSCHRITTE
DER CHEMIE ORGANISCHER
NAT URSTOFFE
PROGRESS IN THE CHEMISTRY
OF ORGANIC NATURAL PRODUCTS
PROGRES DANS LA CHIMIE
DES SUBSTANCES ORGANIQUES
NA. TURELLES
HERAUSOEGEBEN. VON EDITED BY REDIaE PAR
L. ZECHMEISTER
CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA
ELFTER BAND ELEVENTH VOLUME ONZIEME VOLUME
VERFASSER AUTHORS AUTEURS
A. ALBERT· K. BROCKNER • R. B. COREY' K. FREUDENBERG
H. H. INHOFFEN . R. LEMBERG· L. PAULING· S. PEAT
H. SCHMID· W. A. SCHROEDER
MIT 67 ABBILDUNOEN WITH 67 ILLUSTRATIONS AVEC 67 ILLUSTRATIONS
WI EN· S P R I N G E R. V E R LAG· 1954
ISBN-13: 978-3-7091-8016-7 e-ISBN-13: 978-3-7091-8014-3
001: 10.1007/978-3-7091-8014-3
ALLE RECHTE, lNSBESONDERE DAS DER tlBERSETZUNG
IN FREMDE SPRACHEN, VORBEHALTEN
Softcover reprint of the hardcover 1s t edition 1954
Inhaltsverzeichnis.
Contents. - Table des matU~res.
Starch: Its Constitution, Enzymic Synthesis and Degradation.
By STANLEY PEAT, Department of Chemistry, University College of
North 'Vales, Bangor, Caernarvonshire ................ , ............ .
I. Introduction...................................................... 2
II. Chemical Investigations of the Basic Structure of Starch .... . . . . . . . . . 4
I. End-Group Assay .............................................. 4
2. The Molecular Size of Starch.................................... 5
III. Amylose and Amylopectin.. ... .... ...... ... ... ............ ... ... . .. 6
1. Separation..................................................... 6
2. Comparison of Properties... . . . . . . . . . . . .. . .. . . .. . . . . . . . . . . . . . . . . . 8
a) Solubility.................................................... 8
b) Degree of Polymerisation ..................................... 9
c) Percentage of Non-reducing End-Groups...... . . . . . . . . . . . . . . . . . 9
d) Reaction with Iodine............... . . . . . . . . . . . . . . . . . . . . . . . . . . 9
e) Crystallinity................................................. 10
3. The Amylose-Amylopectin Ratio................ . .......... .... .. 10
IV. Structure of Amylose......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. II
1. Molecular Size.................................................. I I
2. Evidence from Amylolysis............ ............. ....... ... . ... 13
3. Z-Enzyme ..........•.......................................... 14
4. The Maltosaccharides.......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
V. Structure of Amylopectin................ . . . . . . . . . . . . . . . . . . . . . . . . .. 18
1. Molecular Size and Degree of Branching. . . .. . .. .. . . . . . . . . . . . . . . . . 18
2. Nature of the Branch Link. . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3. R-Enzyme, a Debranching Enzyme .............................. 23
4. Conformation of the Amylopectin Molecule. . . . . . . . . .. . . . . . . . . . . . .. 24
VI. Enzymic Synthesis of Starch....................................... 25
I. Synthesis of Amylose.............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
a) The Donor.................................................. 26
b) The Acceptor........... ............... ........... ........... 26
c) The Enzyme..................... . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29
2. The Synthesis of Amylopectin ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
a) The Branching Enzyme............. . . . . . . . . . . . . . . . . . . . . . . . . . . 30
b) The Mechanism of Branching........ ...... ... ............. .... 30
c) Substrate for Q-Enzyme...................................... 31
d) Q-Enzyme, a Transglucosylase ................................ 32
e) The Acceptor.......................... . . . . . . . . . . . . . . . . . . . . . . 32
f) D-Enzyme................................................... 33
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
IV Inhaltsverzeichnis. - Contents. - Table des matii~res.
Neuere Ergebnisse auf dem Gebiete des Lignins und der Ver-
holzung. Von K. FREUDENBERG, Chemisches Institut der UniversWi.t
Heidelberg. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
I. Einleitung ...................................................... 43
II. Der Stoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 44
III. Analyse und Reaktionen ......................................... 46
IV. Abbau.......................................................... 49
V. Modellsubstanzen ................................................ 51
VI. Optisches Verhalten... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .. 52
VII. Biosynthese des Lignins . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . ... .. . . . . . . 55
VIII. Vorstufen der Ligninbildung. Die sekundaren Bausteine .. '" . . . . . . . . 60
IX. Verkniipfung der sekundaren Bausteine zum Lignin..... ......... ... 64
X. Beziehung der natiirlichen Ligninarten untereinander und zum kiinst-
lichen Lignin.................................................... 66
XI. Die Bindung des Lignins im Bolze................................ 67
XII. Der Vorgang der Verholzung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
XIII. SchluBwort...................................................... 74
Litera turverzeichnis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 75
Probleme und neuere Ergebnisse in der Vitamin D-Chemie.
Von H. H. INHOFFEN und K. BRUCKNER, Organisch-chemisches
Institut der Technischen Hochschule Braunschweig .................. 83
I. Pracalciferol, ein neues Isomeres in der Reihe der Bestrahlungsprodukte
des Ergosterins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 83
II. Konstitution des Vitamins D2 und des Tachysterins . . . . . . . . . . . . . . . . 87
III. Zusammenfassung neuerer Einzelergebnisse aus der Chemie der Vitamine
und Provitamine D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
I. Neue Verbindungen des Vitamins D2 ........................... 90
2. Neuere Methoden zur Darstellung von Provitaminen und Vitaminen D 91
3. Neue Vitamine D und Beitrage zum Zusammenhang zwischen Kon-
stitution und physiologischer Wirkung . . . . . . . . . . . . . . . . . . . . . . . . . . 93
IV. Ozon-Abbau des Vitamins D2 ; zugleich ein Beitrag zur Stereochemie der
Steroide ........................................................ 95
V. Isomerisierung des Vitamins D2····.·····.········.····· .... ·.·... 97
VI. Synthetische Versuche in der Vitamin D-Reihe ..................... 102
I. Modellversuche zur Darstellung Vitamin D-ahnlicher Substanzen... 102
2. Partialsynthese von zwei neuen Isomeren des Vitamins D2 .•....•• 108
3. Syntheseversuche des C,D-Hydrindan-Ringsystems ................ II2
VII. Photodehydro-ergosterin .......................................... II5
VIII. SchluBwort...................................................... 118
Literaturverzeichnis ............................................ II8
Inhaltsverzeichnis. - Contents. - Table des matieres. V
Natiirlich vorkommende Chromone. (Mit Anhang tiber weitere Eleu-
therine-Inhaltsstoffe.) Von H. SCHMID, Chemisches Institut der Uni-
versitat Zurich ................................................... 124
I. Einleitung ....................................................... 125
II. Pflanzlicher Ursprung und Isolierung der Chromone ................. 126
Ammi visnaga 126. - Peucedanum Ostruthium 127. - Eugenia
caryophyllata 127. - Eleutherine bulbosa 127. - Isolierung der
Chromone 127.
III. Konstitutionsermittlu~g der Chromone . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 127
I. Allgemeine Bemerkungen ....................................... 127
Abbau mit Alkali 127. - Reaktionen der 2-standigen Methyl-
gruppe 128. - Farbreaktionen 129. - Reaktion mit Carbonyl-
reagenzien 129.
2. Spezieller Teil ....•........................................... 129
Chromone aus Eugenia caryophyllata: Eugenin 129. - Eugenitin 130.-
Isoeugenitin 131. - Isoeugenitol 131. - Umlagerungen mit Jod-
wasserstoffsaure 131. - Chromon aus Peucedanum Ostruthium:
Peucenin 131. - Chromone aus Ammi visnaga: Khellin 133. -
Visnagin 134. - Visamminol 136. - Khellinol 136. - Khellolglucosid,
Khellol 137. - Konstitution und U. V.-Absorptionsspektren von
y-Benzopyronen 137. - Chromon aus Eleutherine bulbosa: Eleutherinol
138.
IV. Synthese der naturlichen Chromone und verwandter Verbindungen ... 140
I. Allgemeine Bemerkungen ....................................... 140
2. Spezieller Teil ................................................ 142
Chromone aus Eugenia caryophyllata 142. - Peucenin 142. - Khellin
und Khellinon 143. - Khellol 145. - Visnagin, Visnaginon und
verwandte Verbindungen 147. - Isovisnagin 148. - Allovisnagin 148.
- Weitere Furo- und Dihydrofuro-chromone ISO.
V. Zur Biogenese der Chromone ..................................... 150
VI. Pharmakologie und therapeutische Anwendung einiger Chromone ..... 154
Khellin 154. - Visnagin ISS. - Khellol-glucosid ISS. - Visammi-
nol 155. - Khellinol ISS. - Visnagan ISS. - Klinische Verwendung
von Khellin ISS.
VII. Zusammenhange zwischen Konstitution und pharmakologischer Wirk-
samkeit von Chromonen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 156
Anhang: VIII. Weitere Inhaltsstoffe aus Eleutherine bulbosa und einige damit
verwandte Verbindungen ......................................... 157
Eleutherol 158. - IX-Sorinin und IX-Sorigenin 160. - p-Sorinin und
p-Sorigenin 161. - Weitere naturliche Naphthaline 161. - Eleu-
therine-chinone und Fusarubin: Eleutherin 162. - Isoeleutherin 165.
- Allo-eleutherin 166. - Alloiso-eleutherin 166. - Konfigurative
Zusammenhange 166. - Fusarubin 170.
Literaturverzeichnis ......••.......•................................ 172
VI Inhaltsverzeichnis. - Contents. - Table des matieres.
The Configuration of Polypeptide Chains in Proteins. By LINUS
PAULING and ROBERT B. COREY, California Institute of Technology,
Pasadena, California ............................................... 180
Introduction ...... '. ................................................... 181
1. The Dimensions of the Amide Group ............................... 182
I. The Amino Acids .............................................. 182
a) The Crystal Structure of L-Hydroxyproline .................... 182
b) The Crystal Structure of DL-Serine ........................... 186
2. Simple Pep tides and Related Substances ......................... 188
a) The Crystal Structure of ex-Glycyl-glycine .................... " 188
b) The Crystal Structure of N,N'-Diglycyl-L-cystine Dihydrate ..... 190
c) The Crystal Structure of Glycyl-L-asparagine .................. 193
d) The Crystal Structure of Glycyl-L-tryptophan Dihydrate........ 195
3. The Configuration of the Amide Group .......................... 196
a) Dimensions of the Amide Group .............................. 196
b) Effects of Resonance ......................................... 199
c) Properties of N-H· . ·0 Hydrogen Bonds ..................... 200
d) Estimations of Stabilization and Strain Energies ............... 202
II. Helical Configurations of Polypeptide Chains . . . . . . . . . . . . . . . . . . . . . . .. 204
I. The ex Helix ............................................ . . . . . .. 204
2. The y Helix and Other Helixes .................................. 207
III. Sheets of Polypeptide Chains ...................................... 209
IV. The Structure of Fibrous Proteins .................................. 213
I. The Structure of the ex-Keratin Proteins ......................... 215
a) Some Interpretations of the X-ray Pattern .................... 217
b) The Occurrence of the ex Helix ............................... 220
A. Synthetic Polypeptides 220. - B. The ex-Keratin Proteins 222.
2. The Structure of Silk and the fJ-Keratin Proteins ................. 2'25
3. Collagen and Gelatin ........................................... 227
V. The Structure of Globular Proteins ................................. 228
Refere.nces .......................................................... 234
Column Chromatography in the Study of the Structure of Pep-
tides and Proteins. By W. A. SCHROEDER, California Institute of
Technology, Pasadena, California. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 240
Introduction .......................................................... 241
1. The Separation of Amino Acids and the Determination of the Amino Acid
Composition of Peptides and Proteins............................... 242
I. Analytical Determination of Amino Acids by Chromatography.. . . .. 242
a) Separation of Amino Acids on Starch ......................... 242
b) Separation of Amino Acids on Ion Exchange Resins ............ 246
c) Comparison and Discussion of Starch and Ion Exchange Methods 246
d) Application of Starch and Ion Exchange Methods to the Analysis
of p,.ptides and Proteins ..................................... 250
2. Isolation of Amino Acids by Chromatography ..................... 255
a) Method of HIRs, MOORE, and STEIN .......................... 256
b) Method of PARTRIDGE and Collaborators ....................... 258
c) Miscellaneous Isolative Methods ............................... 260
3. Conclusions .................................................... 260
Inhaltsverzeichnis. - Contents. - Table des matieres. VII
II. The Determination of Amino Acid Sequence in Proteins. The Identification
of Terminal Residues and the Separation and Identification of Peptides 261
I. Identification of N-Terminal Amino Acids ........................ 262
a) SANGER'S Method: The Use of 2,4-Dinitroiluorobenzene ......... 262
b) EDMAN'S Method: The Use of Phenylisothiocyanate ............. 269
c) Other Methods .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 271
d) Conclusions ................................................. 271
2. Identification of C-Terminal Amino Acids ........................ 272
a) The SCHLACK and KUMPF Method. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 272
b) The Carboxypeptidase Method ................................ 274
c) Reduction Methods ................................. , ........ 275
d) The Hydrazinolytic Method .................................. 275
e) Conclusions ................................................. 276
3. The Separation and Identification of Peptides .................... 276
a) The Separation of Free Peptides .............................. 277
b) The Separation of DNP-Peptides .............................. 281
c) The Identification of Peptides ................................ 282
d) Conclusions .................................................. 282
III. The Separation and Purification of Proteins ......................... 283
IV. Concluding Remarks .............................................. 287
References .......................................................... 288
Porphyrins in Nature. By R. LEMBERG, Institute of Medical Research,
The Royal North Shore Hospital, St. Leonards, Sydney.............. 299
I. Introduction . 300
II. The Structure of the Porphin Nucleus ............................ 301
III. The Naturally Occurring Porphyrins ............................... 306
IV. Methods of Isolation, Separation, Identification and Estimation ...... 310
Isolation of Porphyrins from Natural Sources .................... 310
Separation ................................................... 310
Solubility .................................................. 310
HCl-Method ................................................ 311
Crystallisation .............................................. 3 II
Chromatography ............................................ 311
Identification of Porphyrins .................................... 312
Absorption Spectra ......................................... 312
Fluorescence Spectra ........................................ 314
Estimation .................................................. 314
V. Individual Porphyrins ........................................... 314
Protoporphyrin "IX" .......................................... 314
Mesoporphyrin "IX" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 316
Deuteroporphyrin "IX" ........................................ 316
Haematoporphyrin "IX" ....................................... 317
Chlorocruoroporphyrin .......................................... 317
Porphyrin a (Cytoporphyrin) ................................... 318
Cryptoporphyrins .............................................. 320
Mono-, Di-, and Tricarboxylic Porphyrins of Unknown Structure .. 320
Coproporphyrins .............................................. 320
Porphyrins with five to seven Carboxyl Groups.................. 323
VIII Inhaltsverzeichnis. - Contents. - Table des matieres.
Uroporphyrins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 323
Colourless Precursors of Uroporphyrins .......................... 325
Porphyrins derived from Chlorophyll ............................ 328
VI. The Biosynthesis of Porphyrins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 329
VII. The Biosynthesis of Chlorophyll.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 336
VIII. Porphyrins are not Intermediates in the Catabolism of Haem Compounds 337
References .......................................................... 337
The Pteridines. By ADRIEN ALBERT, Department of Medical Chemistry,
The Australian National University, Canberra ........................ 350
I. Introduction..................................................... 351
II. Simple Mono- and Di-substituted Pteridines as Models for the Under-
standing of Naturally-occurring Pteridines ........... " ............. 352
1. Solubility and Fusibility...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 352
2. Stability to Acids and Alkalis .................................. 355
3· Ionization; Metal-binding Properties ....•........................ 356
4· Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 360
5. Chemical Reactions ............................................ 366
III. The Naturally-occurring Pteridines (excluding the Folic Acid Series) .. 366
1. Glossary of Synonyms ......................................... 367
2. The Xanthopterin Family: Xanthopterin, Chrysopterin, Erythropterin 367
Xanthopterin 367. - Chrysopterin 369. - Erythropterin 369.
3. The isoXanthopterin Family: isoXanthopterin, Ichthyopterin,
Fluorescyanine and Leucopterin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 370
isoXanthopterin 370. - Ichthyopterin 370. - Fluorescyanine 370.
- Leucopterin 371.
4. Substances closely Related to the Naturally-occurring Pteridines:
Pterorhodin, Urothion.......................................... 371
Pterorhodin 371. - Urothion 372.
IV. The Folic Acid Series ............................................ 372
1. The Synthesis of Pteroylglutamic Acid ("PGA").................. 373
2. The Occurrence and Properties of Pteroylglutamic Acid ........... 377
3. Conjugates of Pteroylglutamic Acid .............................. 380
4. Rhizopterin ................................................... 382
5. The Citrovorum Factor and Leucovorin .......................... 382
6. New Members of the Folic Acid Series .......................... 385
V. Substances which are Presumably Pteridines ........................ 385
VI. Chromatography and other Techniques of Isolation and Purification.. 388
VII. The Physiological Action of the Natural Pteridines .................. 389
The Simpler Pteridines ........................................... 389
The Folic Acid Series............................................. 39 I
References ................................. , .. , .... '" .............. 392
Namenverzeichnis. Index of Names. Index des Auteurs .................. 404
Sachverzeichnis. Index of Subjects. Index des Matieres .................. 422
Starch: Its Constitution,
Enzymic Synthesis and Degradation.
By STANLEY PEAT, Bangor, U. K.
With 4 Figures.
Contents. Page
1. Introduction 2
II. Chemical Investigation of the Basic Structure of Starch.............. 4
I. End-Group Assay .............................................. 4
2. The Molecular Size of Starch ................................. .'.. 5
III. Amylose and Amylopectin.......................................... 6
I. Separation .................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Comparison of Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S
a) Solubility.................................................... S
b) Degree of Polymerisation ..................................... 9
c) Percentage of Non-reducing End-Groups ......................' . 9
d) Reaction with Iodine......................................... 9
e) Crystallinity ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3. The Amylose-Amylopectin Ratio................................. IO
IV. Structure of Amylose.................................. . . . . . . . . . . .. II
I. Molecular Size.................................................. I I
2. Evidence from Amylolysis....................................... 13
3· Z-Enzyme ...................................................... 14
4. The Maltosaccharides .........................................' . .. 16
V. Structure of Amylopectin........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IS
I. Molecular Size and Degree of Branching. . . . . . . . . . . . . . . . . . . . . . . . .. IS
2. Nature of the Branch Link......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3. R-Enzyme: a Debranching Enzyme.. .. . .. ... . . . .. .. .. . . . .... . ... 23
4. Conformation of the Amylopectin Molecule.. . . . . . . . . . . . . . . . . . . . . .. 24
VI. Enzymic Synthesis of Starch....................................... 25
I. Synthesis of Amylose .................................. ,........ 26
a) The Donor ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 26
b) The Acceptor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 26
c) The Enzyme................................................. 29
2. The Synthesis of Amylopectin.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29
a) The Branching Enzyme... . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 30
b) The Mechanism of Branching. ...... ....... ... ... .. ......... . .. 30
Fortschritte d. Chern. org. Naturst. XI.
2 S. PEAT:
c) Substrate for Q-Enzyme...................................... 3 T
d) Q-Enzyme: a Transglucosylase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 32
e) The Acceptor................................. . . . . . . . . . . . . . . . 32
f) D-Enzyme................................................... 33
References.......................................................... 34
1. Introduction.
I t is interesting to speculate on the unique position occupied by
D-glucose in the life processes of both animals and plants. We cannot
yet begin to understand why the constitution and configuration of this
sugar should fit it to play the predominating role it does. The facts remain
that glucose is the only sugar found in the blood of animals and that
enzymic mechanisms exist in animal tissues for the conversion of almost
every other monosaccharide into glucose. In the plant the story is similar,
but here glucose is associated with the closely related ketose, D-fructose
and the disaccharide, sucrose. It would appear that glucose and fructose
are interchangeable in many of the sequences of plant metabolism.
Indeed, interconversion of glucose and fructose in plants is an established
fact and the enzyme system responsible has been closely studied. In the
majority of plants the energy derived from photosynthesis is stored as
carbohydrate and the most abundantly distributed representative of
this class of reserve carbohydrate is starch, a polyglucose. Polymerised
fructose (fructosans) is by no means an unusual mode of storage and
in some plants, e. g. sugar cane or beet, the favoured form of storage is
sucrose.
Glucose is more than a vehicle of energy, it is a structural unit also,
inasmuch as the basic constituent of the cell walls of all higher plants
is cellulose which, like starch, is built entirely of glucose units. For the
carbohydrate chemist interested in the metabolism of plants, glucose
is the focal point but the raw material for chemical investigation would
obviously be the polysaccharides, starch and cellulose, since these are
synthesised every year in enormous quantities by vegetation all over
the globe.
From the metabolic point of view, starch is of greater significance
than cellulose. The latter is a skeletal material, giving strength and
rigidity to plants, and once it has been laid down in the cell walls very
little happens to it until the plant dies. Starch, on the other hand, comes
and goes. The resting cereal seed or potato is gorged with it but when
the seed germinates or when the potato sprouts, the starch is rapidly
converted into forms which can be directly assimilated by the growing
and respiring plant. It is the purpose of this article to review the attempts
that have been, and are being, made to elucidate the interrelated problems