カイコ5齢幼虫由来の葉酸代謝酵素 : conjugaseとdihydrofolate reductaseの性質

概要

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Some properties of folic acid γ-glutamyl hydrolasc (conjugase) [EC 3.4.22.12] and dihydrofolate reductase [EC 1.5.1.3] in silkworm larval bodies were investigated. The conjugase enzyme had an optimum pH of 7.8, and an optimum temperature of 50℃. The enzymatic activity was stimulated in the presence of 2-mercaptoethanol, K^+ and Mg^<2+>, but inhibited by p-hydroxymercuriphenyl sulfonate, Co^<2+>, Zn^<2+> and Fe^<2+>. This conjugase converted pteroylpenta-γ-L-glutamic acid to pteroyl monoglutamic acid exclusively, and the Km value was about 9.6mM when measured at pH7.8, 37℃ with pteroyltriγ-L-glutamic acid as the substrate. The dihydrofolate reductase in the silkworm fat body required NADPH, had an optimum pH of 4.5〜7.5, and an optimum temperature of 35℃. Its actvity was stimulated in the presence of 2-mercaptoethanol, guanidine, Mg^<2+> and high concentration of K^+ and Na^+, but inhibited by p-chloromercuribenzoate, formamide and Co^<2+>. The Km value measured at pH5.0, 30℃, was about 2.7mM when dihydropteroyl glutamic acid was used as the substrate.
日本ビタミン学会の論文
2000-12-25