ISSN:
1432-072X
Keywords:
Key words Malonyl-CoA:acetate CoA transferase
;
Na+ transport decarboxylases
;
Na+ cycle
;
Citrate lyase
;
Citramalate lyase
;
CoA-like prosthetic group
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Malonate decarboxylation by crude extracts of Malonomonas rubra was specifically activated by Na+ and less efficiently by Li+ ions. The extracts contained an enzyme catalyzing CoA transfer from malonyl-CoA to acetate, yielding acetyl-CoA and malonate. After about a 26-fold purification of the malonyl-CoA:acetate CoA transferase, an almost pure enzyme was obtained, indicating that about 4% of the cellular protein consisted of the CoA transferase. This abundance of the transferase is in accord with its proposed role as an enzyme component of the malonate decarboxylase system, the key enzyme of energy metabolism in this organism. The apparent molecular weight of the polypeptide was 67,000 as revealed from SDS-polyacrylamide gel electrophoresis. A similar molecular weight was estimated for the native transferase by gel chromatography, indicating that the enzyme exists as a monomer. Kinetic analy ses of the CoA transferase yielded the following: pH-optimum at pH 5.5, an apparent Km for malonyl-CoA of 1.9 mM, for acetate of 54 mM, for acetyl-CoA of 6.9 mM, and for malonate of 0.5 mM. Malonate or citrate inhibited the enzyme with an apparent Ki of 0.4 mM and 3.0 mM, respectively. The isolated CoA transferase increased the activity of malonate decarboxylase of a crude enzyme syst em, in which part of the endogenous CoA transferase was inactivated by borohydride, about three-fold. These results indicate that the CoA transferase functions physiologically as a component of the malonate decarboxylase system, in which it catalyzes the transfer of acyl carrier protein from acetyl acyl carrier protein and malonate to yield malonyl acyl carrier protein and acetate. Malonate is thus activated on the enzyme by exchange for the catalytically important enzyme-bound acetyl thioester residues not ed previously. This type of substrate activation resembles the catalytic mechanism of citrate lyase and citramalate lyase.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002030050100
Permalink
