脳に於ける蛋白代謝—局所生化学的観点より

Protein Metabolism of the Brain: A topobiochemical study

　脳に於ける局所生化学を考える場合一応2つに分けて考えることが出来る。1つは所謂局所生化学，即ち大脳，小脳などと云う局所の生化学的特性を比較研究するものであり，他の1つは細胞内に於ける局所生化学とも云うべきもので脳神経細胞内の各微細構造の比較研究を目的とするものである。前者に就ては1930年代に既にPeters，Dixon，Himwich等によつてin vitroで呼吸が調べられて以来多数の研究が行われ酵素の分布や種種の物質の分布が報告されている。最近に於てはラジオオートグラフがこの方向に応用されて一層精細な分析が行われる様になつた。後者に就てはSchneider等によつて肝臓の遠沈分画法が確立されて以来脳にも応用され1950年に入つてRichter，Abood，Brody等によつて酵素や核酸の核，ミトコンドリア，マイクロブームに於ける分布が研究報告された。最近上記の2つの方向の研究は統一されて例えば大脳皮質小脳等に於ける細胞生化学と云う形で研究される様になり既にFurst等^1）によつてその蛋白代謝が報告されている。

　筆者等は以上の観点より脳に於ける蛋白代謝に就て脳の各局所に於ける比較と大脳皮質細胞内の各微細分画に於ける比較とを検討したので以下に述べようと思う。

The rate of the incorporation of 2-C¹⁴-glycineinto the proteins varied in different parts of thebrain. This was shown in experiments, in whichspecific activity of the proteins of various areaswas studied after injection of 2-C¹⁴-glycine to ratsor rabbits by the subarachinoid or intracisternalroute. It was found that the uptake of 2-C¹⁴-glycine into the proteins of rat brain areas was inthe following order: Cerebellum＞Thalamus＞Cerebral cortex＞Midbrain＞Cerebral white matter＞Medulla oblongata＞ Spinal cord. In rabbitsthe highest rate of incorporation was observed inthe Amygdara. There was a marked incorporation in the Hypothalamus, in the Hypocampus, inthe Cerebellum (grey and white matter), and inthe Cerebral cortex. The rate of incorporationinto the proteins of Nucl. caudatus and G. cinguriwas relatively lower as compared with that ofother areas. Cerebral white matter always showedlower activity than cerebral grey matter. Thisfinding was further confirmed by in vitro experiments employing tissue slices. The content of theamino acid activating enzymes of ginea-pig brain,observed by PP-ATP exchange reaction, was inthe following order : Cerebellum＞Cerebral cortex＞Medulla. The incorporation of 2-C¹⁴-glycineinto isolated particles which was obtained frombrain tissue by differential centrifugation, wereestimated both in vivo and in vitro. The proteinsof the microsomal fraction were labelled mostrapidly in short period after 2-C-¹⁴-glycine injection in vivo, however, after 30 min. those ofsupernatant fraction showed the highest specificactivity. In in vitro experiments the proteins ofthe supernatant fraction were labelled most rapidlythrough out the experimental period, followedthose of microsomal and nucleal fraction. Thesefindings in vitro were further confirmed by employing U-C¹⁴-leucine.