Inhibitory effects of pentagalloylglucose on the respiratory chain of Photobacterium phosphoreum.

The activity of glucose-dependent oxygen consumption of whole cells of Photobacterium phosphoreum was inhibi6ted by purified pentagalloylglucose (1, 2, 3, 4, 6-penta-O-galloyl-β-D-glucose). Sonicated membrane vesicles were used to study the effect of the inhibitor on the electron transport activity. The activity of reduced nicotinamide adenine dinucleotide (NADH) oxidase in sonicated membrane vesicles of P. phosphoreum decreased when pentagalloylglucose was added to the assay system. The results suggested that the targets of inhibitory action were NADH dehydrogenase and terminal oxidase.The effect of the inhibitor on the terminal oxidase was compared in the case of purified terminal oxidase (cytochrome bd complex) and sonicated membrane vesicles. The oxidase activities toward ubiquinol-1 and N, N, N', N'-tetramethyl-p-phenylenediamine dihydrochloride (TMPD) in the presence of ascorbate were both inhibited by pentagalloylglucose in sonicated membrane vesicles and purified cytochrome bd complex. The inhibition of ubiquinol-1 oxidase activity in sonicated membrane vesicles and purified enzyme was of noncompetitive type. On the other hand, the inhibitions of TMPD plus ascorbate oxidase in both membrane vesicles and purified enzyme were uncompetitive. Thus, the mechanisms of inhibition of the two kinds of oxidase activities by the inhibitor were different.The inhibitory effect of tetragalloylglucose (1, 2, 3, 6-tetra-O-galloyl-β-D-glucose) on the respiratory chain was similar to that of pentagalloylglucose in the case of membrane vesicles and purified enzyme.