1. Two nitroreductase enzymes of the liver which are responsible for the reductions of nitro and nitroso groups respectively, were isolated separately and purified by the aid of DEAE-cellulose.
2. Several properties of the two enzymes have been studied; Both enzymes are active at pH 7.8. DPNH is about ten times active than TPNH as the hydrogen donor for both of the enzyme reactions, Nitroreductase is inhibited by oxygen, whereas nitrosoreductase is quite insensitive to oxygen. Both of the enzyme actions are inhibited by several metal-chelating agents, suggesting that they are both metallo-proteins. The enzymes are con-sidered to have the active sulfhydryl groups from the inhibitory studies.
3. Nitroreductase was found to be a flavoprotein which specifically utilize flavin-adenine dinucleotide as hydrogen carrier, whereas the flavin nucleotides are considered not to be necessary for the reduction of nit-rosophenol by the nitrosoreductase.
The author wishes to express many thanks to Prof. K. Honda for his kind guidance throughout this work.
The author's thanks are also due to Prof. K. Okunuki, Prof. S. Akabori of Osaka University, and Prof. R. Sato of the Institute for Protein Re-search, Osaka University, for their excellent advices and encouragements.
The author is further indebted to Prof. K. Narita of the Institute for Protein Research for his generous gifts of the ion exchangers.

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1. Streptomyces griseus proteinase (Pro-nase) catalyzed a limited proteolysis of native ovalbumin in to plakalbumin-like protein.
2. Two peptide fragments, Ala-Ala and Ala-Gly-Val-Asp were liberated. Relative velocities of the both liberation were approxi-mately 2:1.
3. The Pronase-modified ovalbumin pos-sessed one serine as the N-terminal and migrated as slightly less acidic protein than the original one by paper electrophoresis.
4. These results were discussed.

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Acetylenic mercuric compounds of general formulae (R-C_??_C)₂Hg and R-C_??_C-Hg-R' were found to be highly effective in inhibit-ing spore germination of a plant pathogenic fungus, Cochliobolus miyabeanus. This anti-fungal activity was shown to be reversed in the presence of glutathione.
This fact suggests that those mercurials may be active against sulfhydryl enzymes as is the case in the other known organo-mercuric compounds. It was, however, shown that some of those, acetylenic mercuric com-pounds were almost ineffective against β-amylase of sweet potato and alcohol dehydro-genase of baker's yeast and slightly effective against jack bean urease. The ineffectivity of such mercurials against sulfhydryl enzymes is discussed.
The author wishes to express his deep gratitude to Prof. T. Yanagita of Chiba University and Prof. A. Takamiya of University of Tokyo for their kind guidance and encouragement throughout this work. Thanks are due to Mr. M. Matsui, Director, and Dr. Y. Miura of this laboratory for their kind encouragement. The author greatly appreciates the kindness of Dr. I. Iwai of this laboratory for his supply of acetylenic mercurials.

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1. The stoichiometric studies on the reaction of diphenethynyl mercury and gluta-thione were carried out spectrophotometrical-ly. It was found that 1 to 2 moles of the mercurial and glutathione, respectively, gave I mole of diglutathionyl mercury and 2 moles of phenylacetylene. These final prodocts were always found to be produced, independent of the initial molar ratios of these two reac-tants.
2. Kinetical studies performed on this reaction system revealed that a first-order reaction was rate-limiting process on the mole-cule of diphenethynyl mercury and that more complicated reaction process occurring on glutathione molecule. Possible reaction schemes on this reaction system are presented.
3. The spectrophotometric method was also applied to the study on the reactivity of diphenethynyl mercury with urease protein. It was concluded that diphenethynyl mercury reacted easily with “reactive” sulfhydryl groups of urease protein, whereas it reacted slowly with “sluggish” ones. This view was further supported by the fact that diphenet hynyl mercury exhibited only a partial inhibition on the ureolytic activity of urease; the cite of enzymatic activity of this enzyme has been known to be involved in the reac-tivity of the “sluggish” sulfhydryl groups in the protein molecule.
The author wishes to express his deep gratitude to Prof. T. Yanagita of Chiba University and Prof. A. T akamiya of University of Tokyo for their kind guidance and encouragement throughout this work. Thanks are due to Mr. M. Matsui, Director, and Dr. Y. Miura of this Laboratory for their kind encouragement, and to Dr. S. 0saki of Tokyo Institute of Technology for his technical guidance in ultracentrifugation.
The author is indebted to Messrs. T. Onoe, O. Amakasu, and H. Higuchi, and to Misses C. Furukawa and H. Ohtsuka of this Labora-tory, for elemental analyses and infrared spectral measurements.

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1. When L-lysine was oxidized by L-lysine oxidase to δ-aminovaleric acid in a medium in which the molecular oxygen was labeled with O¹⁸, at least one atom of molecular oxygen was incorporated into the product isolated from the reaction mixture.
2. A chemical exchange between the carboxyl group and the oxygen in the medium resulted in a dilution of O¹⁸ abundance ratio of the enzymatically produced δ-aminovaleric acid.
3. When the enzymatic oxidation of L-lysine was performed in a medium containing H₂O¹⁸, an apparent incorporation of O¹⁸ into o-aminovaleric acid was observed. It is pos-sible that this was an artifact due to the exchange reaction occurring during the isolation procedure.
This investigation was supported in part by a research grant from the National Institutes of Health, United States Public Health Service (C-4222) and a Scientific Research Grant from the Ministry of Edu-cation of Japan to one of us (O. H.).

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1. Acetone-soluble lipid was isolated from a large amount of human erythrocytes and was fractionated by silicic acid column chromatography.
2. It was separated into cholesterol, cholesterol ester, triglyceride, free fatty acids and non-saponifiable matter.
3. Chemical nature and amount of component fatty acids were determined by reversed-phase chromatography.
4. Non-saponifiable matter other than cholesterol were divided by alumina column, from which cholesta-3, 5-dien-7-one, 7-keto-cholesterol and 7-hydroxy- cholesterol were detected.
The authors wish to express their gratitude to Dr. M. Kit a n o of Nihon Blood Bank & Co. for the supply of human blood cells.
The expenses for the work was aided by the Scientific Fund furnished by the Ministry of Education, for which the authors wish to thank.

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The initial stage of actin polymerization caused by KCl and MgCl₂ was studied main-ly by means of the light scattering. Below a certain critical salt concentration, the mole-cular weight, of G-actin is a constant value of dimer, 117, 000, regardless of the salt con-centration, while the virial coefficient becomes smaller with the increase in the salt concent-ration. These results indicate that the unit of active actin is a dimer, having two poly-merization sites, and that the depression of charge effects is an essential condition of the G-F transformation. Above this critical salt concentration, the G-F transformation begins at a critical actin concentration. Below this critical concentration of actin, the apparent molecular weight is greater than that of the dimer. This suggests that some parts of actin have already polymerized to a certain degree before the initiation of the G-F transformation; when the concentration of these polymerized actins reaches a critical value, then G-F transformation starts.

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Making use of pig thyroid slices, various phases of iodine metabolism and effects of thyrotropic hormone (TSH) upon them were studied, and the following results were obtained.
1. Intrathyroidal iodide pool size does not change during incubation in spite of the presence of active iodide transport and release of iodide.
2. Conversion of iodide to protein-bound iodine was found to occur slowly, but lasted for rather long time. Newly formed protein-bound iodine exists as monoiodo- and diiodo-tyrosines in thyroglobulin molecules.
3. Labeled organic iodine, i.e., monoiodo-and diiodotyrosines, iodinated lipid and thyronine-like substances, are released from slices after prolonged incubation.
4. During initial period of incubation, TSH definitely stimulates the conversion of intrathyroidal iodide to thyroglobulin-bound iodine without affecting the total iodine uptake. The effect decreases with duration of incubation.
5. The change in specific radioactivity of iodine in slices and medium as well as conversion rates of iodine transfer were calculated in the presence and absence of TSH.
The author wishes to express his gratitude to Prof. N. Ui for his guidance in the course of the work. He is also indebted to Dr. M. Nomoto, Institute of Physical and Chemical Research, for the gift of “Pronase” and to Taiyo Gyogyo Kaisha Ltd. for the supply of whale pituitaries. The expense of this study was defrayed in part by a grant from the Ministry of Education.

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1. Thyrotropic hormone (TSH) enhanced the process of the conversion of iodide to protein-bound iodine when pig thyroid slices were incubated with TSH for a short period. It was proved that TSH-sensitive reaction was iodination of thyroglobulin.
2. Specificity of this reaction was con-firmed since three different preparations showed the same effect and serum albumin or ACTH had no effect.
3. The extent of the conversion of iodide to protein-bound iodine was proportional to the logarithm of TSH concentration, though the slope of the dose-response curve conside-rably varied with glands from which slices were prepared.
4. Anti-thyroid compounds and other reagents affected the iodine transfer and the TSH effect in various manners.
The author wishes to express his sincere thanks to Prof. N. Ui for his guidance and encouragement during this work. The expense of this study was defrayed in part by a grant from the Ministry of Education.

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1. A method for the determination of amines in tissues is described.
2. The apparent content of ethanolamine of rat hepatoma and rat regenerating liver was about 8 times greater than that in normal liver.
3. The ethanolamine content increased in parallel with the mitotic rate during liver regeneration.
4. The difference in the ethanolamine content of these tissues was attributed to an enzymatic reaction which produced free etha-nolamine. Addition of an equal volume of acetone to a tissue homogenate almost com-pletely inhibited this reaction in normal liver, while inhibition by acetone was small in homogenates of regenerating liver.
The authors wish to thank Prof. M. Kuru, the Director of this Institute, and Prof. S. Akabor i of the Institute for Protein Research, Osaka University, for their continuous encouragement and interest in this work, and Drs. T. Fukui and S. Morishita for their co-operation in histological work. Thanks are also due to Misses T. Miyaji and C. Iwasaki for their skilled technical assistances.

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1. Under biotin-deficient conditions, B. macerans showed only slight activity in β-hydroxybutyrate dehydrogenation.
2. Addition of DPN or other known cofactors were unable to recover the depres-sed activity in β-hydroxybutyrate dehydro-genation.
3. Experiments with mixed normal and biotin-deficient extracts indicated that the reduced activity was not due to the presence of any inhibitor or to the lack of a heat stable cofactor.
4. HBA dehydrogenating enzyme of this bacteria was determined to belong to β-hydroxybutyryl CoA dehydrogenase which needs DPN as a cofactor.
5. Avidin did not affect the HBA de-hydrogenating activity.
6. In this bacteria biotin probably takes a part in the biosynthesis of the apoenzyme(s) which dehydrogenates HBA.
The authors are particularly indebted to Prof. Shozo Tanaka for his discussions and encourage-ment during this investigation, and also wish to express their thanks to Miss. Tsuya Yoshida for her collaboration.

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