Human gyrate atrophy of the choroid and retina was found to accompany hereditary deficiency of ornithine oxoacid aminotransferase (EC 2.6.1.13) and hyperornithinemia. I have maintained to study ornithine metabolism of rat liver for long time, but recently have turned to study ocular ornithine metabolism using special experience in this field and reached some etiological aspects. Contents : I. Ocular ornithine metabolism II. Nature of ocular ornithine oxoacid aminotransferase III. Properties of purified ∇^1_pyrroline-5-carboxylate reductase from bovine retina IV. Biochemical studies on retinal degeneration using retinal degeneration mouse as a model of the gyrate atrophy of the choroid and retina We have found the occurrence of active ornithineproline pathway, which is first catalized by ornithine oxoacid aminotransferase and secondary by pyrroline-5-carboxylate reductase, in the retinas of mouse and cow and probably it also exists in human retina. In C3H retinal degeneration mouse, we found a marked decrease of pyrroline-5-carboxylate reductase activity and ornithineproline converting activity in the retina after 10th postnatal day. Since this pathway seems to be a sole endogenous proline suppliant in the retina, the deficiency of ornithine oxoacid aminotransferasc in the gyrate atrophy should bring a deficiency of proline supplement to the some critical locus in the retina.

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The enzymatic property of pyridoxaminephosphate oxidase (EC 1.4.3.5: pyridoxarninephosphate: oxygen oxidoreductase (deaminating)) purified from various sources so far, was compared with each other. It was discussed whether the enzyme could utilize PMP or PNP as the true substrate in the PLP production in vivo. A11 the enzymes could oxidyze two naturally occurring vitamin B6 derivatives, PMP and PNP, but the relative activity for PNP to PMP, was considerably different from origin to origin. The enzyme purified from baker's yeast was the most specific one for PMP so far investigated. The ratio of PNP oxidase to PMP oxidase at 285 μM substrate concentration was about 0.25:1 in 0.2 M Tris-HCI buffer (pH 8.0). However, the ratio was altered to about I . I : I in 0.2 M Hepes-KOH buffer (pH 8.0) after the enzyme preparation was dialyzed against the same buffer. The pyridoxinephosphate oxidase activity found in wheat seedlings was separated into two fractions when the crude, acid-treated preparation was subjected to a DEAE-Sephadex A-50 column. These two fractions, suggesting to be isozymes, were significantly different from each other in enzymatic property as well as in the mobility on electrophoresis. One fraction was considerably specific for PNP, being associated with only about 10% of its activity for PMP.

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ミエリン形成時期以前からNiA欠乏飼料で飼育したラットの脳では,ミニリン含量が低下し,ミエリン脂質の長鎖脂肪酸の割合が低下する原因を明らかにすることを試みた. 1)生後12目目に離乳したのち,NiA欠乏飼料叉はNiA添加飼料で飼育したラットに経時的に<14>^C-acetateを腹腔内注射L,脳及び肝臓の脂質に取り込まれた放射活性を測定した.NiA欠乏飼料及びNiA添加飼料で飼育したラットともに肝臓の脂肪酸合成は成長するに従って増加したが,脳の脂肪酸合成はミエリン形成の時期を過ぎると急激に低下した. 2)NiA欠乏飼料叉はNiA添加飼料で飼育したラットの脳をスライスにし,Krebs-Ringer bicarbonatebuffer中で<14C>-acetateとともにincubateして脂質に取り込まれた放射活性を測定すると,NiA欠乏飼料群ではNiA添加飼料群に比べて低下していた. 3)NiA欠乏飼料叉はNiA添加飼料で飼育したラット脳の脂肪酸合成に関与する酵素の活性を測定すると,fatty acid synthetase活性には両群の間で差は見られたかったが,fatty acid e1ongating enzymeの活性はNiA欠乏飼料群ではNiA添加飼料群に比べて低下していた. これらの結果から,NiA欠乏飼料で飼育したラットの脳ではミエリンの形成が抑制されるのは,ミエリン形成期に増加する脳の脂肪酸の合成,特に長鎖脂肪酸の合成が抑制されるため,ミエリン脂質の構成成分として必要た長鎖脂肪酸の不足によるものと推測された.

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