Advances in Enzymology and Related Areas of Molecular Biology, Volume 12

574 Pages·1951·18.904 MB·English

ADVANCES IN ENZYMOLOGY
AND RELATED SUBJECTS OF
BIOCHEMISTRY
Volume XI1
CONTRIBUTORS TO VOLUME XI1
PETERB ERNFELDD,e partment of Surgery, Cancer Research and Cancer Control
Unit, Tufts College Medical School, Boston 11, Massachusetts
FREDERICKCH ALLENGEDRe, partment of Organic Chemistry, The University,
Leeds 2, England
BRITTONC HANCET, he Eldridge Reeves Johnson Foundation for Medical Physics,
University of Pennsylvania, The School of Medicine, Philadelphia 4, Pennsylvania
G. C. GIBBONSS,h irley Institute, Manchester 20, England.
ROBERTH ILLA, gricultural Research Council Unit of Plant Biochemistry, School of
Biochemistry, Cambridge University, Cambridge, England
KURTH . MEYERL, aboratoire de Chimie Organique de 1’ Universitd, Geneva, Switzer-
land
DAVIDN ACHMANSODHeVpa,r tment of Neurology, College of Physicians and Sur-
geons, Columbia University, New York 32, New York
EMILL . SYITH,U niversity of Utah College of Medicine, Salt Lake Cify, Utah
MERTONF . UTTER, Department of Biochemistry, Western Reserve University
Medical School, Cleveland, Ohio
IRWINB . WILSOND, epartment of Neurology, College of Physicians and Surgeons,
Columbia University, New York 32, New York
HARLANDG . WOOD, Department of Biochemistry, Western Reserve University
Medical School, Cleveland, Ohio
CHARLESA . ZITTLE,E astern Regional Research Laboratory, Philadelphia 18,
Penns yloania
ADVANCES IN ENZYMOLOGY
AND RELATED SUBJECTS OF BIOCHEMISTRY
Edited by F. F . NORD
FORDHAM UNIVERSITY, NEW YORK, N. Y.
VOLUME XI1
NEW YORK
INTERSCIENCE PUBLISHERS LTD.. LONDON
Copyright, 1951, by
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CONTENTS
Oxidoreduction in Chloroplasts. By ROBERT HILL, Cambridge, EngrcCnd
1
I. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . .............. 1
11. Production of Oxygen by Cell-Free Prep
111. Oxygen-Producing Reaction of the Chloroplast. . . . . . . . . . . . . . . . . . . . 2
6
IV. Some Properties of the Photochemically Active Chloroplast Material
9
V. Properties of the Elements Iron and Magnesium in Tetrapyrrolic
Compounds.. . . . . ..._......_........ 13
VI. Hematin Compounds
21
VII. Effect of Inhibitors o
.......................
25
28
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3317
Addendum ..................................................
39
Mechanisms of Fixation of Carbon Dioxide by Heterotro hs and Auto-
trophs. B MERTON F. UTTER and HARLAN8 G. WOOD,
Cleveland, 8hio. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......
41
I. Introduction.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
11. BeAta. -CBaertbao-Cxyarlabtoioxny l.a tion in Dicarbox.y.l.i.c. .A.c.i.d.s... .. .. .. .. .. .. .. .. ... ..... . 5500
Occurrence Reactions Synthesizing Dicarbox
21.. Roflreo omf ACaTrPbo ofi nn tDhieo Oxixdaela..c e. t.a . R..e.a.c.t.io.n... .. .. .. 52
Fixation of Carbon Dioxide by the “Malic Enzyme”. . . . . . 54
3. 61
Relationship Oxalacetate Carboxylase and “Malic En-
4. of
zyme” ...........................................
63
arboxylase
. . . . . . . . .
6. Role of Pyruvate in Oxalacetate Synthesis. . . . . . . . . . . . . . 6738
Effect of Cofactors, Ions, and Amino Acids on Oxalacetate
87.. BioCtainrb aonxydl aCsaer .b .o .n . .D . i.o .x .i d. e. .F . i.x .a .t .i o. .n ... . .. .. .. .. .. I. .. .. .. .. .. .. . . . . . 80
Summary.. . . . . . 81
B. Be9t.a -Carboxylation in .................. 85
1. General Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8866
Demonstration Fixation in Tricarboxylic Acids.
111. AlAph. aI-nCt23ar..o r bdSouuxcmytilmoatnaio.r .ny ,.. .. ... . . .. o..f .. .. . .. .. .. . .. .. .. . . .. .. . .. .. .. . .. .. .. . .. .. .. .. .. .. .. .. . . . .. . 89999222
1. General Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9933
2. Fixation of Carbon Dioxide in Pyruvate by Butyl Alcohol
PhBosapchteorrioac.l .a .s .ti .c . .R . e. a.c . t.i o. n. . i.n . .E .s .c ,h .e .r i.c .k .i a. .c .o .l .i .. . . . . . . . .. .. .. .. .. .. .. 94
3. 95
C. Carbon Dioxide Fixation by the Dismutation Reaction.. . . . . .
D. Carbon Dioxide Fixation in Alpha-Ketoglutarate.. . . . . . . 101
E. Summary ... . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
106
V
vi CONTENTS
Mechanisms of Fixation of Carbon Dioxide by Heterotrophs and Auto-
trophs (continued)
IV. CaArb. oSny Dntihoexsiidse oFf iAxacteitoicn Ainc iAd dfjraocmen Ct aCrabrobno nD iAotxoimdes... .. .. .. .. .. .. .. .. .. .. .. .. .. 110067
1. Introduction.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
2. Recent Investigations of Fixation of Carbon Dioxide by
Clostridium thermoaceticum . . . . . . . . . . . . . . . . . . . . . . . . . . 110
3. Fixation of Carbon Dioxide by Diplococcus glycinophilus . . 119
4. Fixation of Carbon Dioxide by Clostridium acidi urici. . . . 121
5. Fixation of Formaldehyde in the Propionic Acid Fermenta-
tion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
6. Summary ........................................... 128
B. Ca1r.b oInnt Droidouxicdteio Fni.x. a.t .i .o .n . i.n . .P .h .o . t.o .s .y .n .t .h .e .s .i s. .. .. . . . . . . . .. .. .. .. .. .. .. .. .. .. ., .. 112299
2. Fixation of Carbon Dioxide in the 3 and 4 Positions of
Sugars ........................................... 130
3. Phosphoglyceric Acid and Photosynthesis. . . . . . . . . . . . . . . 131
The Question of General Reducing Agents from the Light
4.
Reaction ......................................... 132
5. Evaluation of the C14 Methods.. . .............. 135
6. Results from 138
7. Summary.. . 143
References . . . . . . . . . . ...... . . . .. ,, ... 145
Enzyme-Substrate Compounds. By BRITTON CHANCE, Philadelphia,
Pennsylvania . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
1I1.. IPnhtyrsoidcaulc atinodn .C. h.e . m. . i.c .a .l .P . r.o . p. e.s. o.f. .E.n.z.y..m.e.-.S.u..b.s.tr.a.t.e. .C.o.m..p.o..u.n.d.s . . 11..5543~
A. Absorption Spectra. . . . . . . . . . . . . . . . . . . . . . . 154
B. Valence and Bond Type of the Iron Atom of
Compounds ............................ 157
C. Stoichiometry of the Reaction of Enzyme and 159
D. Dissociation Constants of Enzyme-Substrate 159
ns for the Reaction of
.. 161
111. Kinetic Studies of Enzyme-Substrate Compounds. . . . . . . . . . . . . . . . . 163
A. Introduction .................... 163
of Enzyme and Subst 163
C. Molecular Statistics of the Combination of Enzyme and Sub-
strat ....................................... 164
D. Revers ation of Enzyme-Substrate Complexes. . . . . . 165
E. Spontaneous Decomposition of Enzyme-Substrate Complexes. . 165
F. Reaction of Enzyme-Substrate Complexes with Donor Molecules 166
G. Ternary Complexes of Enzyme-Substrate and Donor Molecules 168
IV. StuBAd..i eSMsu oebft shEtornadztsey a mannded A DDceotfinivnoiitrty iS opanenscd.i. f .Si c.p i.et .yc . i o.f fi. c .Ci .ta y.t ..a. l.. a ..s ,.e ..s .. a.. n.. .d. .. P.. e.. r..o .. x .. i..d ..a ..s ..e .s. ... ... 1~11777.11 ~4
C. Mechanism of Catalysis of the Reverse Reactions.. . . . . . . . . . . 175
D. Multiplicity of Enzyme-Substrate Complexes. . . . . . . . 176
E. Heme Linkages and Activity.. . . . . . .. . . . . . . . . . . . . . . . . . . . . . 178
F. Why Are Ferrimyoglobin- and Ferri obin-Peroxide Com-
plexes Relatively Inactive?. . . . . . ................. 180
G. Oxidation of Dihydroxymaleic Acid oxi d a s es . . . . . . . . . . . 181
H. The Mechanism of Catalase Action.. . . . . . . . . . . . . . . . . . . . . . . . 182
I. The Question of Valency Change.. . . . . . . . . . . . . . . . . . . . . , 184
J. The Study of the Kinetics of Enzyme-Substrate Compounds in
Dehydrogenase Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
V. RPheyfesrioenlocgeisc.a .l .F .u . n. .c .ti .o .n . .o .f .C . .a t.a .l .a .s e. s. .a .n .d . .P .e .r .o .x .i d. a. s.e .s . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. 118885
vii
CONTENTS
The Specificity of Certain Peptidases. By EMIL L. SMITH, Salt Lake
City, Utah. ..... . . . . . .._...._....................1 91
I. Introduction and Classification. . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
11. Leucine Am~opeptidase 196
A. Role of Metal Ion.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
B. Specificity ............................................... 200
1. Amino Acid Amides, Dipeptidcs.. . . . . . . . . . . . . . . . . . . . . . 200
2. Dipeptide Amides.. . . . . . . . . . . . , . . . . . . . . . . . 204
C. Distribution.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
111. Aminotripeptidase.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
IV. Yeast Polypeptidase. . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
V. Glycylglycine Dipeptidase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VI. Glycyl-L-leucine Dipeptidase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VVIIIII.. PCraorlnidoasisnea. s.e .. .. . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 22 1
IX. Pancreatic Carboxypeptidase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
BA.. SGpeenceirfaicl iPtyr .o.p.e .r.t.i .e s. . . . . ., .. .. .. ... .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. . . .. .. .. .. .. .. .. .. ..
Groups ............................
2. Optical Specificity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. The Sensitive Bond. Esterase Action.. . . . . . . . . . . . . . . . . 228
4. Influence of Amino Acid Residues. :. . . . . . . . . . . . . . . . . . . 229
5. Action on Derivatives of Unnatural Amino Acids.. . . . . . .
6. Effect of Bond Strength and the Secondary Bond.. . . . . . .
C. Action of Inhibitors.. . . , . . , . . . . . . . . . , . . , . . , . . . . . . . . . , . . . .
1. Effect of Metal-Combining Agents.. . . . . . . . . . . . . . . . . . . . 238
2. Structural Inhibitors. . , . . . . . . . . . . . . . . . . . . . . . . . . . . 243
D. Kinetics ................................................
X. Some General Considerations. . . . . . . . . . . . . . . . .
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Enzymic Hydrolysis and of Acetylcholine. By DAVID
Synthesis .
NACHMANSOHN and IRWIN B. WILSON, New York, New York.. 259
I. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . , . . . . . . . . 259
11. General Features of Acetylcholinesterase . . . . . . . . . . . . . . . . . . . . . . . . . 262
A. Methods of Determination.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
B. Specificity 264
C. Ubiquity in Conducting Tissue. . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
D. Distribution and Localization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 1
E. Preparation and Purification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
FG.. FInrheeib Eitnoersrg. .y . C. . h. a.n . g. o.li.n.e. .H.y.d.r.o.l.y.s.i.s. . .. .. ., .. .. .. .. .. .. .. .. 227779
111. Mechanism of Reactions Catalyzed by Acetylcholirlesterase. . . . . . . .
A. Intermolecular Forces between Enzyme and Substrate. . . . . . . .
B. The Hydrolytic Process.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV. Synthesis of Acetylcholine.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 31 1
A. The Acetylation Problem. . . . . . . . . . . . . . . . . . . . . , , . . . . . . . . . , 311
B. Discovery of Choline Acetylase and of the Energy Source of
Acetylation . . . . . . . . . . . . , . . . . . . . . . . . . . . . , . . . . . . . . . , . . . . 312
C. Int_eg:ation of Acetylcholine in the Met:holic Cycle of the Xerve
C;Cll 315
D. Preparation of the Enzyme.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
E. Components of the System and Optinutl Conditions of Activity 318
F. Inhibitors ...._.. . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . , . 322
G. Occurrence ..... . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . .
. ........................
..........................................
........................ ,. 331
References. . . . . . . . . . . ............ . . . . . . . 334
viii CONTENTS
. .
The Present Status of Starch Chemistry By KURT H MEYER. Geneva.
Switzerland. and G . C . GIBBONS. Manchester. England ...............
341
I11. . HSeisptaorraitciaoln I onft rSotdaurccthio inn t.o. .A.m..y.l.o.s.e. .a.n.d. .A.m..y.l.o.p.e.c.t.in.. ........................ ... 3.4~~ 2
A . Review of Methods ........... 343
. 343
B Experimental Procedure ..................................
. 344
Preparation Amylose A1 ............................
21 . Solution of thofe Residue ............................... 344
3.. PPrreec iapriatatitoionn o fo f AAmmyylolo seec tAin2 ....................... ............... 334454
I11 . Quantita4t ive &timation of AmyEse in Starch .................... 345
. 345
A Potentiometric Titration of Amylose ........................
B . Colorimetric Assay of Amylose ........... 346
IV. Control of Amylose Purity by Degradation with 347
A. Experimental Procedure .................................. 348
. Reagents .................................... ... 350
21 . Standard Curve ..................................... 350
. Photometric Determination of &Amylase Activity ....... 350
34.. Checking the Absence of a-Amylase in &Amylase ........ 33.55.10
Degradation ........................................
V . Behavio5r of Amylose in Water ...... ........................ 351
. 351
VI Addition Products of Amylose ..................................
. 353
VII Constitution of Amylopectin ....................................
A. Degree of Branching ....................... ........... 353
B . Nature of the Branch Linkages. ........................... 353
. 355
C Form of the Molecule .............. .............
. 356
VIII Reactivity of Amylopectin ...........
. 357
IX Molecular Weight of Amylose and Am
. 359
A Experimental Procedure ........
X . The Starch-Iodine Complex ......... 360
. 363
XI Investigation of Starch and Its Deriva
Polarized Light ...........................
XI1. Submicroscopic Structure of the Starch Granule an 365
nomena ....... ..................................
367
367
368
369
. 370
XV Glycogen ................................
XVI . Dextrins ................................ 371
372
References ...................................................
374
.
of Starch Degradation and Synthesis By PETER BERNFELD.
EnBzyosmteons. Maaaachusetts. .......... ........................
379
I . Introduction ...................................................
. 380
11 The Substrate .................................................
. 380
A Heterogeneity .......... ..........................
B. Solubility .............. 380
C . Existence of the Native 381
. 38 1
I11 Hydro1 tic Enzymes .................. ...............
A. dydrolysis of Glucosides ................................... 381
B. Am1y .la Hseiss .to.r.i.c.a.l. ............................... ... ........................ 33_3888122_ ~
.
2 Phenomena Observed during n ........... 383
. Existence and &Amylases .......................
3. Measuremeofn t a- Amylase Activity ..................... 383
4. Action a-Amofy lase ................................. 385
56. Action ooff @-Amylase. ................................ 386
. Occurrence Amylases ............. ......... 391
7 of 395
CONTENTS ix
Enzymes of Starch Degradation and Synthesis (continued)
.
8 Pure Crystalline Amylases. ........................... 396
9 . Purity Tests for Crystalline Amylases .................. 401
10. Comparison of Pure Amylases with Each Other ......... 404
11. Specificity and Affinity ............................... 406
12. Conclusions Derived from the Properties of Pure Amyl-
ases .............................................. 408
13. Amylase Inhibitors ... ......................... 408
.
C Amyloglucosidases ........................................ 409
1. a-l,4-Glucosidases .................................... 409
2 . a-1 ,6 -Glucosidases .................................... 409
IV. Transglucosidases (Nonhydrolytic Enzymes) ............. 410
A. Definition ................................................ 410
.
B Pho.s phorylases ........ ....... I ............ 412
1 Introduction ......................................... 412
2 . Action of Phosphorylases .............................. 412
.
3 The Individual Phosphorylases ................... 414
4 . Comparison of the Phosphoryla th Each Other ....... 416
5. Isophosphorylase ...................... 417
.
C Nonphos horolytic Transglucosidases ........................ 419
1. Cycyodextrinase. ..................................... 419
.
2 Amylomaltase ........................................ 420
.
3 Amylosucrase ........................................ 421
4 . Q-Enzyme ........................................... 4~~ 21~
D . Unidentified Transglucosidases ....... ....... ...... 423
1. Branching Factor ..................................... 423
2 . Amylose Isomerase ................................... 423
E . Synthesis of Starch .................... ....... 424
References .................................................... 424
.
Biological Methylation By FREDERICK CHALLENGER, Leeds,
England ......................................................... 429
I . Alkylarsonic Acids and Scopulariopsis brevicaulis ................ 432
. Methylation of Inorganic Compounds of Selenium and Tellurium . . 433
I1 .
I11 Methylating Capacities of Other Penicillia ...................... 435
IV. Fission of the Disulfide Link in Dialkyl Disulfides by Scopulariopsis
brevicaulis and Methylation of the Alkyl Sulfur Group ......... 436
n the Nature of Mycological Methylation .......... 437
de Link by Molds and in Other Bio
............................... 438
VII. Behavior of Thiourea and Thiouracils in Cultures of Scopula
brevicaulis ................................................ 441
VIII. Natural Products Derived from Dimeth 1 Sulfide ................ 443
.
IX Identification of the Precursor of Dimetlyl Sulfide ............... 445
X . Thetin Salts and Mold Cultures ............................... 446
.
XI Mechanism of Biological Methylation in Molds .............. 447
.
A The Acetic Acid Hypothesis ............................. 447
B . The Formaldehyde Hypothesis ........................... 448
XI1. Possible Origins of Glyoxylic Acid, Formaldehyde, or Related One-
Carbon Compounds in Nature ............................ 449
A. Deamination of Glycine and Breakdown of Serine .......... 449
B . Oxidative Demethylation of N-Methyl Compounds 450
C . Breakdown of Purines through Uric Acid to Glyoxy 451
.
XI11 Transfer of Methyl Groups ................................... 453
A. Transfer of a Methyl Group in Purely Chemical Experiments 453
1.. Mobility of a Methyl Group in Betaine ................ 454
2 Mobility of a Methyl Group in Dimethylthetin ........ 454
.
B The Hypotheses of the Transfer of Methyl by Molds ....... 455
.
1 Methylation of Arsenic, Selenium, and Tellurium Com-
.........................................
pounds 455
X CONTENTS
Biological Methylation (continued)
.
2 Methylation of Sulfur Compounds ........... 457
3 . Methylation of Nitrogen Compounds ................. 457
.
C Alternative Mechanism of Biological Methylation .......... 458
XIV. Transmethylation. Du Vigneaud’s Experiments Using Isotopic In-
dicators ................................................ 458
A . Choline and Methionine ................................. 458
.
B Mono- and Dimethylaminoethanols as Possible Methyl
Donors ..................... ..................... 462
C . Transmethylation from Betaine . .................. 463
XV. Transmethylation by Enzyme Systems in Vz‘itro. ............. 464
XVI. Transmethylation from Derivatives of Cysteine and Methionine 467
A . Keto Derivatives ....................................... 467
B . Oxidized Derivatives of Methionine ....................... 467
XVII . Synthesis of Labile Methyl in the Body ........................ 469
XVIII . Methylated Derivatives of Pyridine and Quinoline .......... 474
XIX. Later Work on the Metabolism of Methionine .................. 478
XX. Biological Oxidation of Methyl Groups ......................... 480
.................... 480
.................... 481
e Thetins ............. 481
D . Biochemical Stab e Methyl Groups of Creatine and
............................. 481
.
XXI Biological Importance of the Thetins ............................ 482
References ............................... .... 486
.
Reaction of Borate with Substances of Biological Interest By CHARLES
A. ZITTLE. Philadelphia. Pennsylvania ............................. 493
I . Introduction .................................................. 493
I1 . Reaction of Borate with Simple Polyhydroxy and Related Compounds 494
-
A . TvDes of ComDounds Givine Reaction ....................... 494
B . Ty“1p es of Complexes Formed ................................ 496
C . Change in Properties of Polyhydroxy Compounds ............. 499
D . Equilibria Involved . Reversibility .................... 501
I11. Reaction of Borate with Polysaccharides . ................... 502
A. Vegetable Gums and Mucilages ............................. 502
1 . Vegetable Gums and Mucilages That React with Borax .... 502
2 . Factors that Influence Complex Formation ..............
3 . Complex Formation in Nonaqueous Solvents. ............
4 . Complex Formation with Tannin and Polyvinyl Alcohol ...
5 . Nature of the Borate-Polysaccharide Complex ............
.
B Blood Group Substances ........... .............. 509
1. Isolation of Blood Group Subst h Borate .......... 509
2 . Change in Properties in the Presence of Borate ........... 511
3 . Component Monosaccharides Probably Responsible for
Reaction .......................................... 513
.
C Bacterial Polysaccharides ................................. 513
.
IV Reaction of Borate with Vitamins and Other Substances That Are
Components of Coenzymes .................................. 514
.
A Adenosine 5-Phosphate (Muscle hdenylic Acid). .............. 514
.
B Pyridoxine (Vitamin Be) ....................... ...... 515
C . Riboflavin (Vitamin Bs) .................................... 515
D . Dehydroascorbic Acid ..................................... 516
V. Effects of Borate on the Activity of Certain Enzymes ............... 516
A . Polyhydroxy Compound as Coenzyme or Substrate ............ 516