Bacillus subtilis (Bs) citrate synthase (CS)-II_like. CS catalyzes the condensation of acetyl coenzyme A (AcCoA) and oxalacetate (OAA) to form citrate and coenzyme A (CoA), the first step in the citric acid cycle (TCA or Krebs cycle). 2MCS catalyzes the condensation of propionyl-coenzyme A (PrCoA) and OAA to form 2-methylcitrate and CoA during propionate metabolism. The overall CS reaction is thought to proceed through three partial reactions: a) the carbanion or equivalent is generated from AcCoA by base abstraction of a proton, b) the nucleophilic attack of this carbanion on OAA to generate citryl-CoA, and c) the hydrolysis of citryl-CoA to produce citrate and CoA. This group contains proteins similar to BsCS-II, the major CS of the gram-positive bacterium Bacillus subtilis. A mutation in the gene which encodes BsCS-II (citZ gene) has been described which resulted in a significant loss of CS activity, partial glutamate auxotrophy, and a sporulation deficiency, all of which are characteristic of strains defective in the Krebs cycle. Streptococcus mutans CS, found in this group, may participate in a pathway for the anaerobic biosynthesis of glutamate. This group also contains functionally uncharacterized CSs of various gram-negative bacteria. Some of the gram-negative species represented in this group have a second CS isozyme found in another group. This group contains proteins which functions exclusively as either a CS or a 2MCS, as well as those with relaxed specificity which have dual functions as both a CS and a 2MCS.
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