Respiration-coupled glucose transport in membrane vesicles from Azotobacter vinelandii

Abstract

An inducible, carrier-mediated transport system for d-glucose is present in membrane vesicles isolated from Azotobacter vinelandii O. The active accumulation of glucose by these preparations requires the addition of oxidizable substrate: l-Malate produces a 25-fold stimulation of both the rate and steady-state levels of glucose uptake; NADH and NADPH produce a 5-fold stimulation. Phosphoenolpyruvate and ATP, in addition to a number of other metabolites, are without effect. The membrane vesicles oxidize malate to oxalacetate via l-malate dehydrogenase, and the addition of flavin adenine dinucleotide is required for maximal stimulation of glucose transport by malate. Glucose accumulation by the vesicles in the presence of l-malate requires oxygen, and is blocked by electron transport inhibitors and carbonyl cyanide m-chlorophenyl hydrazone, but not by arsenate. These findings indicate that the glucose uptake system is coupled to l-malate dehydrogenase via the respiratory chain of A. vinelandii. However, the generation of high-energy phosphate compounds or the participation of a phosphoenolpyruvate phosphotransferase system is not required for glucose accumulation by the membrane vesicles.