gltA

gltA is the gene name commonly used in bacteria for citrate synthase, the enzyme at the entry point of the citric acid cycle. The encoded protein catalyzes the condensation of acetyl-CoA with oxaloacetate to form citrate, with CoA released as a byproduct. This reaction links glycolysis-derived carbon to central energy metabolism and is essential for aerobic respiration in many organisms.

In many bacteria, gltA encodes citrate synthase I, which typically functions as a homodimer and operates in the cytosol. Some species possess alternative citrate synthase forms (often referred to as class II enzymes) with distinct structural and regulatory properties. Eukaryotes also carry citrate synthase, but in these organisms the enzyme is encoded by nuclear genes and delivered to mitochondria, where it participates in the same core reaction within the tricarboxylic acid cycle.

Regulation of gltA and citrate synthase activity is driven by substrate availability (acetyl-CoA and oxaloacetate) and the cellular energy state. In bacteria, expression of gltA can be controlled at the transcriptional level by carbon source and nutrient status, while enzymatic activity can be modulated by allosteric effectors in some species. The enzyme thus serves as a key control point for flux through the TCA cycle and, indirectly, for biosynthetic pathways that rely on TCA intermediates.

gltA homologs are widespread across bacteria and are related to citrate synthases in mitochondria and plastids, reflecting their conserved role in central carbon metabolism.