Regulatory and structural interrelationships between adenosylcobalamin-dependent ethanolamine ammonia-lyase and the CoA-dependent aldehyde dehydrogenases of Escherichia coli

Abstract

Escherichia coli metabolizes ethanolamine to acetyl CoA via acetaldehyde (Shukla & Turner, 1980). The deamination step is catalysed by cobamide-dependent ethanolamine ammonia-lyase (EAL; EC 4.3.1.7), and the resulting acetaldehyde is further metabolized by CoA-dependent acetaldehyde dehydrogenase (ALDH) (EC 1.2.1.10). EAL is composed of six large structural or regulatory subunits (protein I, mo1.W. 56 900) and six small catalytic subunits (protein 11, mo1.W. 35 200) (Pennington et al., 1981). Induction of EAL requires the concerted action of both ethanolamine and coenzyme B,, (Blackwell & Turner, 1978). Cultures of E. coli type-I (N.C.I.B. 8114) and its derived mutants, N.C.I.B. 11361 and PDT 31, were supplied with nitrogen as either ethanolamine (1 ghitre) plus vitamin B,, (4O,ug/litre), i.e. inducing conditions, or (NH,),SO, (1 ghitre), i.e. non-inducing conditions. Elution from Bio-Gel A-1.5 m of cell-free extracts from type-I cultures grown under inducing conditions produced a peak with both EAL and ALDH activity at an elution volume corresponding to a 'spherical' mo1.W. of 520000 (ALDH isoenzyme A) with a second ALDH peak at 370000 (isoenzyme B). The two co-eluting enzyme activities were separable by anion-exchange chromatography on DEAEcellulose. After this latter step, it was found that the molecular weight of isoenzyme A had fallen to 12OOO0, and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis revealed that this enzyme was a dimer of subunit mol.wt. 58 100. Extracts from E. coli type-I cultures grown under non-inducing conditions contained no EAL activity but significant ALDH activity