Open AccessAcetyl‐coenzyme A synthetase in the thermophilic, acetate‐utilizing methanogen Methanothrix sp. strain CALS‐1
Author(s) -
Teh Yok Lan,
Zinder Stephen
Publication year - 1992
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.1992.tb05481.x
Subject(s) - chemistry , cofactor , pyrophosphate , biochemistry , inorganic pyrophosphatase , methanogen , enzyme , thermophile , strain (injury) , biology , organic chemistry , methane , anatomy
There is considerable evidence that acetyl‐CoA synthetase (acetate thiokinase, ACS, EC 6.2.1) is responsible for acetate activation in the mesophilic acetotrophic methanogen Methanothrix soehngenii . If the pyrophosphate produced by ACS is simply cleaved, two high‐energy phosphodiester bonds are expended in acetate activation. Hi High ACS activity (2–4 μmol min −1 mg protein −1 ) was present in cell‐free extracts of the thermophile Methanothrix sp. strain CALS‐1. The 23‐fold purified enzyme had a molecular mass near 165 kDa and a subunit molecular mass near 78 kDa, suggesting that the enzyme is a homodimer. The temperature optimum for ACS was near 70°C and the apparent K m values were 2–4 mM for acetate and 5.5 mM for MgATP. Coenzyme A at concentrations greater than 0.2 mM inhibited ACS, while acetyl‐CoA was not inhibitory. AMP and pyrophosphate inhibited ACS with K i values of 5 mM and 1.5 mM respectively. Other divalent cations could replace Mg 2+ , with Mn 2+ showing the highest activity. Activity with ITP was 20% of that with ATP, and other nucleotides tested were considerably less active. Since Methanothrix sp. strain CALS‐1 has an active soluble pyrophosphatase, it appears that it uses the same energetically costly method for acetate activation as M. soehngenii .