燐酸モノエステラーゼの賦活と阻害

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Since the middle points of pA-inhibition curves obtained with these compounds were different from one another, being located at pA 2.04, 1.55 and 2.54, respectively, the maximum activities .indicating the tops of these pA-activation curves of bell from were 0.43, 0.87 and 0.34, respectively, when the maximum activity by histidine activation was assumed as 1.00. Their pA-activation curves seem to consist of the imidazole activation curves of second order and the inhibition curves of first order belonging to the imidazole derivatives. The intensity of inhibitory capacities of imidazole derivatives depended on their side chain ・structure. Inhibition by benzoylhistamine was illustrated as a sigmoid curve of first order and coincided . nearly with that of benzoylhistidine. The activating capacity of benzoylhistamine was not ascertainable as well as benzoylnistidine. This fact will mean that the activating capacity ascribable to imidazol nucleus was overshadowed by the inhibition caused by the side, chain devoid of free amino groups. The activation by tyramine was negligible. Cysteine had stronger activating capacity than other sulfur containing amino acid, the ascending part of pA-activation curve being a sigmoid of third order, and the descending part a sigmoid of second order. The ascending branches of the curves obtained with methionine and cysteic acid were sigmoid of second order as was the case with ordinary amino acids, while that in cystine was of first order as was the case with dipeptide. The strong activation by cysteine and its pA-activation curve of third order will be clue to sulfhydryl radical, and the first order pA-activation curve of cystine indicates that this amino acid behaves owing to the presence of disulfide linkage as though it were dipeptide.

燐酸モノエステラーゼIII(アルカリ性フォスファターゼ)のアポ酵素はMg^<++>が存在する時,アミノ酸或はペプチドにより活性化されてホロ酵素を形成するが,このホロ酵素はそれ等賦活剤の過剰により不活性化され,この賦活能発現には原則として遊離のアミノ基,カルボキシル基の存在を必要とされた。しかしprolineに賦活作用があり,ヒスタミンはヒスチジンに比敵する賦活と阻害能を示し,他方ヒスチジン,チロジンのアチル体,さらにイミダゾールにもホロ酵素阻害作用あることが証明されたから,著者はフォスファターゼ賦活,阻害作用にアミノ基,カルボキシル基のほか,なおイミノ基,第3級アミノ基及びhydroxyphenyl基も関係ある事を推論した。これを検討する為にイミノ酸,アミン及び含Sアミノ酸等に就き行つた実験成績を報告する。

The apo-enzyme of. alkaline phosphomonoesterase is activated . in the presence of Mg by various kinds of amino acids or peptides. It seems that the presence of free amino and carboxyl radical is necessary for its activation. But this is not always the case, because, according to K. Kobayashi, proline and histamine have activating capacity. As previously reported, investigations carried out so far has revealed that the acylderivativesof amino acids had shown no activating capacity. On the other hand, the holoenzyme was inhibited by an excess of amino acids or peptides. But the acylamino acids had no inhibting activity. However, acetyl and benzoyl derivatives of histidine and tyrosine exhibited an inhibitory activity. Imidazole also had an inhibitory activity: In the present studies, Co-phosphomonoesterase action of proline was first examined. The pA-activation curve obtained with this amino acid, by plotting the extent of holoenzyme formation against pA, the negative logarithm of the proline concentrations; showed a sigmoid of second order as was the case with other amino acids. Sarcosine manifested the same form of curve. But in the case of this N-methylated amino acid a higher concentration than in glycine was required for activation to the maximum extent. The activating capacity of tryptophane was not strong despite the presence of secondary amino radical in indole nucleus. Choline and betaine had neither activating nor inhibitory action. Imidazole, 4(5)-hydroxymethylimidazole, and acetylhistidine exhibited both actions; the maximum of holoenzyme formation shown by these compounds was 'lower than that attained by histidine. The ascending parts of pA-activation curves obtained with these three imidazole derivatives coincided with one another in position, and, the theoretical middle points of these curves were located at pA 2.65. It seems, therefore, that the activating capacities of imidazole derivatives are almost the same so far as they have no free amino radical on their side chain.