Characterization of activity and expression of isocitrate lyase in Mycobacterium avium and Mycobacterium tuberculosis.

Analysis by two-dimensional gel electrophoresis revealed that Mycobacterium avium expresses several proteins unique to an intracellular infection. One abundant protein with an apparent molecular mass of 50 kDa was isolated, and the N-terminal sequence was determined. It matches a sequence in the M. tuberculosis database (Sanger) with similarity to the enzyme isocitrate lyase of both Corynebacterium glutamicum and Rhodococcus fascians. Only marginal similarity was observed between this open reading frame (ORF) (termed icl) and a second distinct ORF (named aceA) which exhibits a low similarity to other isocitrate lyases. Both ORFs can be found as distinct genes in the various mycobacterial databases recently published. Isocitrate lyase is a key enzyme in the glyoxylate cycle and is essential as an anapleurotic enzyme for growth on acetate and certain fatty acids as carbon source. In this study we express and purify Icl, as well as AceA proteins, and show that both exhibit isocitrate lyase activity. Various known inhibitors for isocitrate lyase were effective. Furthermore, we present evidence that in both M. avium and M. tuberculosis the production and activity of the isocitrate lyase is enhanced under minimal growth conditions when supplemented with acetate or palmitate.

Genetic and biochemical analysis of haemin dependent mutants of Bacillus subtilis.

Numerous porphyrin auxotrophic mutants have been isolated from the 168 trpC2 strain of Bacillus subtilis by selection with streptomycin. Some of them could be supplemented with ALA while the majority grew only in the presence of haemin. Among the latter strains, the syntropism test allowed to distinguish two groups different in phenotype, viz., feeders accumulating ALA and non-feeders accumulating instead of ALA other porphyrin intermediates. On the basis of transductional studies, feeders and non-feeders could be divided into two and four groups, respectively. Biochemical investigation revealed that, with one exception, one enzyme of the porphyrin biosynthesis was coordinated to each hem locus. The following genes were identified:hemB yields ALA-dehydrase;hemC yields PBG-deaminase; hemE yields uroporphyrinogen decarboxylases; hemF yields coproporphyrinogen oxidase; hemG yields protoporphyrin-iron-chelatase.