MEDIUM-CHAIN AND LONG-CHAIN FATTY-ACID UPTAKE AND UTILIZATION BY STREPTOMYCES-COELICOLOR A3(2) - FIRST CHARACTERIZATION OF A GRAM-POSITIVE BACTERIAL SYSTEM

The first characterization of fatty acid uptake in a Gram-positive bac terium is reported. Streptomyces coelicolor A3(2) utilizes fatty acids of different chain length (C-4-C-18) as sole carbon and energy source s. In vivo beta-oxidation studies and the assay of two enzymes of the beta-oxidation cycle proved that fatty acid degradation is constitutiv e in this micro-organism. Uptake of the medium-chain fatty acid octano ate showed the characteristics of simple diffusion, whereas the uptake of palmitate, a long-chain fatty acid, occurred by both simple diffus ion and active transport. After correcting for non-mediated transport, palmitate uptake measured over a wide range of concentrations followe d Michaelis-Menten kinetics. The apparent K-m for palmitate was 97.8 m u M and the V-max was 19.3 nmol min(-1) (mg protein)(-1). Competition experiments showed specificity of the mediated transport component for long-chain fatty acids (> C-10). Metabolic inhibitors such as oligomy cin, NaF and vanadate, and the ionophores gramicidin and carbonyl cyan ide m-chlorophenylhydrazone (CCCP) inhibited palmitate uptake to diffe rent degrees, consistent with the existence of an active transport mec hanism. Uptake rates measured at different ph values indicated that ba th the ionized and the unionized farms of octanoate crossed the cytopl asmic membrane by simple diffusion. Palmitate in its ionized form appe ars to be transported by an active mechanism, whereas the unionized mo lecule diffuses through the membrane. When present in the medium, gluc ose stimulated the degradation of long-chain fatty acids by increasing the rate of uptake and the level of acyl-CoA synthetase.