An acetyl-CoA--S-substituted cysteine N-acetyltransferase in rat liver and kidney preparations was investigated, by using an assay involving incubations with S-benzyl-L-cysteine and [l-14C]acetyl-CoA and extraction of the radioactive product with ethyl acetate. 2. The enzyme was associated with the microsomal fraction and could not be solubilized. Metal ions, EDTA and detergents did not significantly affect the enzyme activity. p-Chloromercuribenzoate and N-ethylmaleimide inhibited the enzyme. 3. Other S-substituted cysteines were acetylated at about the same rate as S-benzyl-L-cysteine. Acetylation of cysteine itself and of methionine, ethionine and tryptophan could be detected but was much slower. Acetylation of aspartic acid, glycine, phenylalanine and serine could not be detected. Palmitoyl-CoA was not a substrate. 4. The enzyme is presumably responsible for the acetylation step of mercapturic acid synthesis; a more physiological function is not yet known, except that the enzyme may be involved in acetylation of those amino acids which occur in elevated amounts in some disorders of amino acid metabolism.
摘要
通过一种检测方法对大鼠肝脏和肾脏制剂中的一种乙酰辅酶A - S - 取代半胱氨酸N - 乙酰转移酶进行了研究，该方法包括用S - 苄基 - L - 半胱氨酸和[1 - ¹⁴C]乙酰辅酶A进行孵育，并用乙酸乙酯提取放射性产物。2. 该酶与微粒体部分相关，且不能被溶解。金属离子、乙二胺四乙酸（EDTA）和去污剂对酶活性没有显著影响。对氯汞苯甲酸和N - 乙基马来酰亚胺抑制该酶。3. 其他S - 取代半胱氨酸的乙酰化速率与S - 苄基 - L - 半胱氨酸大致相同。可以检测到半胱氨酸本身以及甲硫氨酸、乙硫氨酸和色氨酸的乙酰化，但速度要慢得多。未检测到天冬氨酸、甘氨酸、苯丙氨酸和丝氨酸的乙酰化。棕榈酰辅酶A不是底物。4. 该酶可能负责巯基尿酸合成的乙酰化步骤；除了该酶可能参与某些氨基酸代谢紊乱中含量升高的那些氨基酸的乙酰化外，其更生理的功能尚不清楚。
