Satre M, Kennedy E P
J Biol Chem. 1978 Jan 25;253(2):479-83.
Phosphatidylserine decarboxylase, an intrinsic membrane protein of Escherichia coli, catalyzes the decarboxylation of phosphatidylserine, the final step in the biosynthesis of phosphatidylethanolamine, the principal membrane lipid of this organism. The purified enzyme lacks the absorption spectrum characteristic of pyridoxal-containing enzymes, and it has now been found to contain bound pyruvate, the carbonyl function of which is essential for catalytic activity. The decarboxylase is inactivated by treatment with a number of reagents that attack carbonyl groups, including sodium borohydride. Reduction with tritiated borohydride leads to the introduction of stably bound radioactivity, which, after acid hydrolysis, has been identified as tritiated lactate by several chromatographic procedures and by treatment with lactate dehydrogenase. The enzyme resists inactivation by cyanoborohydride in the absence of substrate, but is readily inactivated by this reagent in the presence of phosphatidylserine. Under the conditions of treatment of neutral pH, cyanoborohydride does not react with carbonyl residues at an appreciable rate, but reduces imino groups much more rapidly. This finding, together with demonstrated dependence of the enzyme upon the carbonyl residue of pyruvate for activity, strongly suggests that a Schiff base is formed by addition of the amino group of phosphatidylserine to the pyruvate residue of the enzyme as an essential step in the action of the decarboxylase.
磷脂酰丝氨酸脱羧酶是大肠杆菌的一种内在膜蛋白，催化磷脂酰丝氨酸的脱羧反应，这是该生物体主要膜脂磷脂酰乙醇胺生物合成的最后一步。纯化后的酶缺乏含吡哆醛酶的吸收光谱特征，现已发现它含有结合的丙酮酸，其羰基功能对催化活性至关重要。用多种攻击羰基的试剂处理会使脱羧酶失活，包括硼氢化钠。用氚化硼氢化钠还原会导致引入稳定结合的放射性，经过酸水解后，通过几种色谱方法以及用乳酸脱氢酶处理，已鉴定为氚化乳酸。在没有底物的情况下，该酶能抵抗氰基硼氢化钠的失活作用，但在磷脂酰丝氨酸存在下很容易被该试剂失活。在中性pH处理条件下，氰基硼氢化钠不会以可观的速率与羰基残基反应，但还原亚氨基的速度要快得多。这一发现，连同已证明的该酶活性依赖于丙酮酸的羰基残基，有力地表明，作为脱羧酶作用的一个关键步骤，磷脂酰丝氨酸的氨基与酶的丙酮酸残基加成形成了席夫碱。
