Active Transport in Isolated Bacterial Membrane Vesicles V. THE TRANSPORT OF AMINO ACIDS BY MEllBRANE VESICLES PREPARED FRO3I

Concentrative uptake of 16 amino acids by membrane vesicles isolated from Staphy2ococcus aureus is stimulated 3 to 100 times by the conversion of L-a-glycerol phosphate to dihydroxyacetone phosphate. With the exception of ascorbate-phenazine methosulfate, n-lactate, phosphoenolpyruvate, ATP, and a number of other metabolites and cofactors do not replace or-glycerol phosphate. Amino acid transport by these membrane preparations in the presence of cr-glycerol phosphate requires oxygen, and is blocked by potassium cyanide, sodium azide, and dinitrophenol; however, uptake is not significantly inhibited by high concentrations of arsenate. Vesicles contain insignificant amounts of ATP; and the level of ATP is not increased by incubation in the presence of ol-glycerol phosphate or NADH. The membrane-bound a-glycerol phosphate dehydrogenase is coupled to oxygen via a cytochrome system also present in the vesicle membrane, and spectrophotometric evidence shows that cu-glycerol phosphate dehydrogenase, NADH dehydrogenase, L-lactic dehydrogenase, and succinic dehydrogenase all utilize the same cytochrome system. There is no relationship between rates of oxidation of electron donors by the respiratory chain (NADH > a-glycerol phosphate >> L-lactate=succinate) and the ability of these compounds to stimulate amino acid transport. N-Ethyhnaleimide and p-hydroxymercuribenzoate inhibit amino acid transport and cr-glycerol phosphate oxidation. However, N-ethylmaleimide does not significantly inhibit a-glycerol phosphate dehydrogenase with dichlorophenolindophenol as an artificial acceptor, nor does it inhibit oxygen utilization in the presence of NADH. These findings indicate that the site of coupling of a-glycerol phosphate dehydrogenase to amino acid transport lies between the primary dehydrogenase and the cytochrome chain. It is concluded that amino acid transport in S. aureus is