CITRATE LYASES OF LACTIC-ACID BACTERIA

Citrate lyase is a key enzyme of the citrate metabolism which is invol ved in flavor and texture of many fermented milk products. Citrate lya se which catalyses the cleavage of citrate into oxaloacetate and aceta te is a multienzyme complex composed of three proteins: an acyl carrie r protein (ACP); a citrate, acetate-ACP transferase; and a citryl-S-AC P lyase. The citrate lyase is active only when the thioester residue o f the prosthetic group bound to ACP is acetylated. In the presence of citrate, the transferase mediates the formation of citryl-S-acyl carri er protein by acyl exchange and liberation of acetate. Then the lyase subunit cleaves the citryl-S-ACP with liberation of oxaloacetate and r egeneration of the acetyl-S-ACP. In this review, the actual know ledge on the structure and regulation of citrate lyase in lactic acid bacte ria (LAB) is presented in comparison to the enzymes characterized in o thers micro-organisms. The genetic organization of genes encoding prot eins involved in citrate lyase activity of Leuconostoc mesenteroides i s described. (C) Inra/Elsevier, Paris.