Inhibitory Effects of Tannic Acid on the Respiratory Chain of Photobacterium phosphoreum

Tannic acid inhibited the growth of Photobacterium phosphoreum in liquid culture and also decreased the viability, expressed in terms of the colony forming activity.The activity of glucose dependent oxygen consumption of whole cells was inhibited by tannic acid. It was found that the activity of reduced nicotinamide adenine dinucleotide (NADH) oxidase of the sonicated membrane of Photobacterium phosphoreum decreased when tannic acid was added to the assay system. The results suggested that the targets of tannic acid action were NADH dehydrogenase and the terminal oxidase.The inhibitory effect of tannic acid on the terminal oxidase was compared in the cases of purified terminal oxidase (cytochrome b560-d 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 tannic acid in both sonicated membrane and purified cytochrome b560-d complex. The inhibition of ubiquinol-1 oxidase activity in sonicated membrane was biphasic and noncompetitive in both phases. The inhibition of the ubiquinol-1 oxidase activity of purified terminal oxidase was monophasic and noncompetitive. On the other hand, the inhibition of TMPD oxidase activity in the presence of ascorbate in both membrane vesicles and purified enzyme was uncompetitive. Thus, the mechanisms of inhibition of the two kinds of oxidase activity by tannic acid were different.