VITAMINS

Show abstractHide abstract

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.

View full abstract

Download PDF (1618K)

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.

View full abstract

The effect of nicotinic acid deficiency on myelin lipids which contained high levels of the long chain fatty acid has been studied during brain development. 1. The uptake of intraperitoneally administered 1-^<14>C-acetate was high in the brain but low in the liver of weanling rats. The reverse was noted in the adult animals. 2. The incorporation of 1-^<14>C-acetate into brain lipids was decreased in brain slices of 19 day old rats fed the nicotinic acid deficient diet. 3. The activities of the microsomal palmitoyl-CoA, stearoyl-CoA and arachidyl-CoA elongating enzyme in the nicotinic acid deficient rat were reduced respectively 20, 50 and 50 percent of the rats fed the nicotinic acid supplemented diet. However, the activity of soluble fatty acid synthetase was as active in the nicotinic acid deficient rats as in the nicotinic acid supplemented rats. These observations suggest that nicotinic acid influences the synthesis of long chain fatty acid in the developing rat brain. Therefore, nicotinic acid may play an important role in myelination associated with the synthesis of cerebrosides which contained high levels of long chain fatty acids.

View full abstract

Register with J-STAGE for free!