Rabinovich S E, Nedugova N E, Kagan Z S, Gracheva I M
Mikrobiologiia. 1979 Jul-Aug;48(4):625-31.
A new method of chemical synthesis of alpha-ketoisocaproic acid (the keto analogue of L-leucine) is described. It has been shown that the resting cells of Saccharomyces carlsbergensis 776, in the stationary state of biomass, produce mainly higher alcohols: isobutanol from L-valine and its keto analogue; optically active amylol only from L-isoleucine and its keto analogue; isoamylol only from L-leucine and its keto analogue. "Nonspecific" formation of n-propanol from L-valine, L-isoleucine and their keto analogues, as well as that of isobutanol from L-isoleucine and its keto analogue, has been also found at pH 7.0. Formation of higher alcohols from alpha-keto acids has an acidic pH optimum while that from L-amino acids has a neutral or a weakly alkaline pH optimum. Formation of isobutanol from L-valine is an exception. The dependence of higher alcohol formation on the pH and the kinetics of their accumulation suggest that higher alcohols are produced from L-amino acids in at least three sequential reactions: transamination, decarboxylation of the keto analogue being formed, and reduction of the aldehyde; formation of higher alcohols from alpha-keto acids involves two reactions: decarboxylation and reduction. Transamination and decarboxylation are limiting steps in the process in the former case, and decarboxylation in the latter.
本文描述了一种化学合成α-酮异己酸（L-亮氨酸的酮类似物）的新方法。已表明，处于生物量稳定状态的卡尔斯伯酵母776的静止细胞主要产生高级醇：由L-缬氨酸及其酮类似物生成异丁醇；仅由L-异亮氨酸及其酮类似物生成旋光性戊醇；仅由L-亮氨酸及其酮类似物生成异戊醇。在pH 7.0时，还发现了由L-缬氨酸、L-异亮氨酸及其酮类似物“非特异性”生成正丙醇，以及由L-异亮氨酸及其酮类似物生成异丁醇的情况。由α-酮酸生成高级醇的最适pH为酸性，而由L-氨基酸生成高级醇的最适pH为中性或弱碱性。由L-缬氨酸生成异丁醇是个例外。高级醇生成对pH的依赖性及其积累动力学表明，高级醇至少通过三个连续反应由L-氨基酸产生：转氨作用、生成的酮类似物的脱羧作用以及醛的还原作用；由α-酮酸生成高级醇涉及两个反应：脱羧作用和还原作用。在前一种情况下，转氨作用和脱羧作用是该过程的限速步骤，而在后一种情况下，脱羧作用是限速步骤。
