Arginase, ornithine decarboxylase and S-adenosylmethionine decarboxylase in chicken brain and retina.

Arginase, ornithine decarboxylase and S-adenosylmethionine decarboxylase are active in both retina and brain. Activity is higher in cerebellum than in the cerebral hemispheres and optical lobes. Arginase and ornithine decarboxylase are very active in the retina of very young chicks, while S-adenosylmethionine decarboxylase is poorly active. By contrast, S-adenosylmethionine decarboxylase is much more active in brain. The pattern of activity during development is different; only ornithine decarboxylase is very active during embryonal life; S-adenosylmethionine decarboxylase, at all events in brain, is more active in adult life. Ornithine decarboxylase is inhibited in vitro by alpha-difluoromethylornithine, but not in vivo. Diaminopropane inhibits brain ornithine decarboxylase, but does not induce an ornithine decarboxylase-antizyme. Methylglyoxal bis(guanylhydrazone) promotes an increase of S-adenosylmethionine decarboxylase activity in both the brain and the retina in vivo.

Ornithine decarboxylation in rat liver nuclei.

1. Decarboxylation of ornithine in rat liver cytosol produces putrescine; on the contrary, no putrescine is formed in nuclei. 2. In nuclei, decarboxylation is not inhibited by alpha-difluoromethylornithine and depends on NADH reoxidation. This shows that decarboxylation occurs after transamination of ornithine. 3. The increase of ornithine transaminase activity may be partially responsible for the enhanced decarboxylation after 1-methyl-3-isobutylxanthine administration. Data obtained in the presence of Ca2+ suggest that modification of nuclear Ca2+ concentration may also be responsible.