Hoffmann A, Hilpert W, Dimroth P
Institut für Physiologische Chemie, Technischen Universität München, Federal Republic of Germany.
Eur J Biochem. 1989 Feb 15;179(3):645-50. doi: 10.1111/j.1432-1033.1989.tb14596.x.
Methylmalonyl-CoA decarboxylase of Veillonella alcalescens catalyzed the isotopic exchange between methylmalonyl-CoA and [1-14C]propionyl-CoA or between malonyl-CoA and [1-14C]acetyl-CoA. The exchange was independent of sodium ions and was abolished by avidin. The enzyme also catalyzed the carboxyl transfer reaction from methylmalonyl-CoA to acetyl-CoA yielding propionyl-CoA and malonyl-CoA, and vice versa. The beta subunit was dissociated from methylmalonyl-CoA decarboxylase by prolonged washing of the enzyme while bound via its biotin prosthetic group to monomeric avidin-Sepharose. The beta-chain-depleted enzyme was inactive as a methylmalonyl-CoA decarboxylase but retained carboxyltransferase activity. The beta subunits were specifically protected by Na+ ions from tryptic hydrolysis. Based on these and other observations the following functions may be assigned to the different polypeptide chains of methylmalonyl-CoA decarboxylase: carboxyltransferase (alpha), carboxybiotin-carrier-protein decarboxylase (beta), biotin carrier protein (gamma). The function of the delta chain is unknown.
产碱韦荣球菌的甲基丙二酰辅酶A脱羧酶催化甲基丙二酰辅酶A与[1-¹⁴C]丙酰辅酶A之间或丙二酰辅酶A与[1-¹⁴C]乙酰辅酶A之间的同位素交换。该交换不依赖钠离子，且被抗生物素蛋白抑制。该酶还催化甲基丙二酰辅酶A与乙酰辅酶A之间的羧基转移反应，生成丙酰辅酶A和丙二酰辅酶A，反之亦然。通过用单体抗生物素蛋白-琼脂糖长时间洗涤该酶，β亚基从甲基丙二酰辅酶A脱羧酶上解离，此时该亚基通过其生物素辅基与抗生物素蛋白结合。β链缺失的酶作为甲基丙二酰辅酶A脱羧酶无活性，但保留羧基转移酶活性。β亚基受到钠离子的特异性保护，不被胰蛋白酶水解。基于这些及其他观察结果，甲基丙二酰辅酶A脱羧酶的不同多肽链可能具有以下功能：羧基转移酶（α）、羧基生物素载体蛋白脱羧酶（β）、生物素载体蛋白（γ）。δ链的功能未知。
