A great deal of information regarding the physiology, genetics, and molecular biology of fatty acid and acetate metabolism has been accumulated from studies with E. soli. The use of recombinant DNA technology, coupled with the purification and characterization of enzymes, have enable researchers to correlate the structural genes of the fatty acid degradation (fad) with their respective gene products.
The synthesis of at least five fatty acid-oxidative (FAO) enzymes have been shown to be coordinately induced when long-chain and mediu.m-chain fatty acids (LCFA and MCFA) are present in the growth media. The structural genes encoding these FAO enzymes have been mapped at several sites on the E. soli chromosome to make up fad regulon. This regulon is primarily responsible for the trans-port, acylation, and 8-oxidation of MCFAs and LCFAs. In addition to the FAO enzymes, two degradative enzymes encoded by the atoA and atoB genes appear to be required for the growth on short-chain fatty acids (SCFAs). The glyoxylate shunt enzymes, which are required together with the FAO enzymes for growth of E. soli on fatty acids and acetate, are encoded by ace operon. Among the three structural genes, ace A, ace B, and ace K, the last gene (ace K) codes for the isocitrate dehydrogenase (IDH) kinasephosphatase, which controls the flow of isocitrate via the phosphorylation/dephosphorylation of the Krebs cycle enzyme, IDH.
The fad system has been shown to be requlated by the fad R gene and double regulatory system, fad R and icl R genes, appear to be responsible for the control of glyoxylate shunt enzymes.
|