The carboxyltransferase activity of the sodium‐ion‐translocating methylmalonyl‐CoA decarboxylase of Veillonella alcalescens

Abstract

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 β 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 β‐chain‐depleted enzyme was inactive as a methylmalonyl‐CoA decarboxylase but retained carboxyltransferase activity. The β 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 (α). carboxybiotin‐carrier‐protein decarboxylase (β), biotin carrier protein (γ). The function of the δ chain is unknown. Copyright © 1989, Wiley Blackwell. All rights reserved