カルバミル化合物の水解と合成

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タイトル別名
  • カルバミル カゴウブツ ノ スイカイ ト ゴウセイ
  • Hydrolysis and Synthesis of Carbamyl Compounds
  • 原著
  • Original Article

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諸種カルバミルアミノ酸のうち,カルバミルアスパラギン酸はウラシルの前駆物質としてアスパラギン酸から,またチトルリンは尿素生合成の中間物としてオルニチンから生成され,カルバミルβ-アラニンはウラシル分解代謝産物の一つであることが知られている。私はさきに細菌におけるピリミジン代謝についての実験成績を発表したが,このたびはラットの諸臓器を用いてカルバミルアスパラギン酸,カルバミルグルタミン酸,カルバミルβ-アラニン,カルバミルイソセリン,チトルリンについて,それらの水解および合成の特殊性を実験したのでその成績を報告する。

By homogenate of rat liver carbamyl β-alanine is hydrolyzed producing β-alanine and ammonia, whereas ureidosuccinic acid, ureidoglutaric acid, hydantoic acid and citrulline remain intact. The hydrolytic activity decreases greatly when the liver is autolyzed. Dialyzed liver autolysate catalyzes, however, reversible interchange between carbamyl β-alanine and dihyrouracil, the equilibrium of which is found to be shifted in the direction of opening of the heterocyclic ring. For this test the colorimetric determination of ureido-compounds by Archibald is applied. Therefore, it should be assumed that ureidosuccinic acid once produced in animal cell by carbamylation of aspartic acid is never hydrolyzed, but exclusively anhydrized to dihydroorotic acid for subsequent formation of uridylic acid, while uracil liberated as one decomposition product of ribonucleic acid is reduced to hydrouracil, which is hydrolyzed to carbamyl β-alanine and then to β-alanine. When carbamyl phosphate is used as carbamyl donor, liver autolysate produces citrulline from ornithine, but does not carry out formation of carbamyl aspartate from aspartic acid. On the other hand, homogenate of rat lung forms carbamyl aspartate but no citrulline. Optimum is pH 9 in both cases. Therefore, the carbamylating enzymes for ornithine and aspartic acid, respectively, are different from each other. Other amino acids can not be carbamylated. Carbamyl aspartate synthesis by lung enzyme is not inhibited by glutamic acid, β-alanine, ornithine or cysteinate. This enzyme does not form citrulline from ornithine and even in the additional presence of aspartic acid, ureidosuccinic acid or benzoyl glutamate no spot of citrulline is chromatographically detectable. If the formation of carbamyl aspartate would be carried out actually in vivo in tissues other than liver, the carbamyl donor would be carbamyl phosphate thereto transported from liver.

However, another possibility that transcarbamylation from citrulline to aspartic acid might take place should be considered, though phosphorolysis of citrulline by lung enzyme can not be observed this time.

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