Several concepts have been proposed for the regulation of the regulation of the hydroxylation of 25-hydroxycholecalciferol (25-OH-D_3) in the kidney. The most prominent one is related to whether 25-OH-D_3 is converted to an active metabolite [1,25-(OH)_2-D_3] or to a nearly inert metabolite [24,25-(OH)_2-D_3]. The plasma levels of Ca, P and/or parathyroid hormone (PTH) have been suggested to be directly involved in this kind of metabolic regulation. Our results, however, clearly demonstrate that the regulation can proceed without changes in the plasma levels of Ca, P and possibly PTH, and that the level of 1,25-(OH)_2-D_3 in the body is the major factor which controls the adaptive response of the hydroxylation (1 or 24) of 25-OH-D_3. The regulation by 1,25-(OH)_2-D_3 levels seems to be related to induction or synthesis of 1-or 24-hydroxylases. Plasma levels of Ca, P and/or PTH appear to change the amount of intracellular Ca. The addition of 0.05〜0.2mM Ca to the kidney mitochondrial suspension caused a marked as well as dose-related stimulation of the 1-hydroxylation reaction. This stimulation coincided exactly with the increase in the amount of intramitochondrial Ca. We, therefore, propose that the level of 1,25-(OH)_2-D_3 in the body is related to the induction or synthesis of 1-and/or 24-hydroxylases, and that the amount of intramitochondrial Ca has a key role in the regulation of 1-hydroxylase activity in the kidney.

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The effect of aquocobalamin (OH-B_<12>) on the reaction between electron donors and acceptors under anaerobic conditions was investigated. It was found that the reduction of 2,6-dichlorophenolindophenol (DCIP) and cytochrome c (Cyt. c) by formic acid was accelerated in the presence of OH-B_<12>. OH-B_<12> also accelerated the reduction of methylene blue (MB), thionine and Cyt. c by thiol form of thiamine. Furthermore, it was found that the oxidation of reduced DCIP and Cyt. c under aerobic conditions was accelerated in the presence of OH-B_<12>. From these results, the possibility of the oxidative catalytic activity of cobalamin relating to the biological oxidation was discussed.

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Thiaminase I from Clostridium sporogenes ATCC 8075 was purified 9,100 fold over its culture fluids by the following methods : Norit A treatment, calcium phosphate gel adsorption, ammonium sulfate precipitation, gel filtration and cation and anion exchange column chromatography. The purity of the enzyme preparation in each purification step was checked by means of disc elctrophoresis. The purified enzyme had a specific activity of 61.0 units per mg of protein at pH 8.0,30℃, and the molecular weight determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate was 42,000.

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The decarboxylation of phosphatidylserine to phosphatidylethanolamine was studied in homogenate and subcellular fractions of mouse liver. Among phosphatidylserine decarboxylases of various subcellular fractions, the enzyme of the nucleic fraction was found to be inhibited by various inhibitors to pyridoxal phosphate enzymes. The enzyme of nucleic fraction could be extracted by 2M NaCl solution, and the solubilized enzyme was still more further inhibited by the inhibitors. Deoxypyridoxine also inhibited the enzyme and the inhibition was completely removed by the addition of pyridoxal phosphate. Furthermore, pyridoxal phosphate and Mn^<2+> catalyzed nonenzymatically the decarboxylation of phosphatidylserine to phosphatidylethanolamine. These results seem to show that phosphatidylserine decarboxylase may be pyridoxal phosphate dependent.

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