アオウキクサ（Lemna pausicostata 151）のニコチンアミダーゼの性質ならびに花芽誘導との関連性の考察

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  • アオウキクサ Lemna pausicostata151 ノ ニコチンアミダー

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Biochemical properties of nicotinamidase (EC 3.5.1.19) in a cell-free extract from duckweed (Lemna paucicostata 151) were investigated and considered in relation to the flowering-induction of a plant. As a result, the following properties were confirmed: optimum pH for the reaction: 8.5; maximum reaction velocity was obtained at: 60℃; Km value for nicotinamide: 10.1μM; inhibitors showing more than 50% inhibition at 1mM: Cu²⁺, Hg²⁺, PCMB, nicotinic acid hydrazide, 3-cyanopyridine, benzamide, pyrazinamide, NAD, NADH, NADP, NADPH. It is interesting that the enzyme activity was inhibited by flowering inducers, pyrazinamide and benzamide. No product inhibition by nicotinic acid or ammonium ion was detectable with this enzyme preparation. The reverse reaction, i.e., the conversion of nicotinic acid into nicotinamide in the presence of ammonium ion, glutamine, ATP and magnesium ion, did not occur. From these results, nicotinamidase in the duckweed is thought to play an important role in the formation of trigonelline and NAD. Nicotinamide formed from NAD is accumulated at a certain level in the plant body and flowering may be induced.

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