Abstract
Abstract Glucose transport by membrane vesicles isolated from Azotobacter vinelandii is coupled primarily to malate oxidation via a flavin-linked l-malate dehydrogenase. The addition of flavin adenine dinucleotide is required for malate-dependent glucose transport but is not obligatory for malate oxidation. Both NADH and NADPH are oxidized by the vesicles at rates nearly identical with that of malate yet are only 17% as effective in support of the rate of glucose uptake. Succinate and d-lactate are oxidized at 55 and 20% of the malate rate, respectively. Succinate oxidation does not stimulate glucose transport while d-lactate is 18% as effective as l-malate. However, difference spectra reveal that each of these electron donors is able to reduce almost quantitatively all of the cytochrome components of the membrane preparations. These findings indicate that malate dehydrogenase is coupled to glucose transport at a low potential site which is proximal to ubiquinone. Ascorbate-reduced tetramethylphenylenediamine is oxidized more rapidly by the vesicles than malate and is about as effective as malate in support of the glucose transport rate. This artificial reductant is oxidized via a branch of the respiratory system containing cytochrome c that is blocked by 2 µm cynaide but not by 2-heptyl-4-hydroxyquinoline-N-oxide. Glucose transport that is dependent on this artificial system is inhibited in a similar fashion. However, malate-dependent transport is blocked by the quinoline compound but not by 2 µm cyanide. This reveals a second site of higher potential in the respiratory chain that is linked to glucose transport.
Highlights
These findings indicate that malate dehydrogenase is coupled to glucose transport at a low potential site which is proximal to ubiquinone
Rates of uptake are expressed concentrations of electron donors were employed in the oxygen as percentages of controls
An artificial electron donor system, ascorbatereduced TMPD,i is about as effective as malate in driving glucose uptake, TMPD is oxidized at appreciably higher rates. These results clearly indicate that the relative ability of various electron donors to support glucose transport cannot be accounted for solely by rates of electron flow through the respiratory system of A. vinelundii vesicles
Summary
Azotobacter uinelandii is coupled primarily to malate oxidation via a flavin-linked. L-malate dehydrogenase. DiEerence spectra reveal that each of these electron donors is able to reduce almost quantitatively all of the cytochrome components of the membrane preparations These findings indicate that malate dehydrogenase is coupled to glucose transport at a low potential site which is proximal to ubiquinone. Ascorbate-reduced tetramethylphenylenediamine is oxidized more rapidly by the vesicles than malate and is about as effective as malate in support of the glucose transport rate This artificial reductant is oxidized via a branch of the respiratory system containing cytochrome c that is blocked by 2 PM cyanide but not by 2-heptyl-4-hydroxyquinoline-N-oxide. Membrane vesicles prepared from Azotobacter vinelundii, a strict aerobe, possess an inducible, carrier-mediated transport system for n-glucose [3] Glucose transport by these vesicles is rather coupled to L-malate oxidation via a membrane-associated, flavin-linked malate dehydrogenase. A preliminary report of these findings has been presented [4]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
