Some Effects of Hydrolytic Enzymes on Coupled and Uncoupled Electron Flow in Chloroplasts

Digestion of spinach chloroplasts with pancreatic lipase or trypsin effectively uncoupled electron transport. Continued digestion led to inhibition of saturated rates of Hill reaction activity and a decrease in quantum yield. Irradiation with ultraviolet light decreased the quantum yield and inhibited Hill activity, but did not uncouple. Ascorbate-dichlorophenol-indophenol-mediated reduction of nicotinamide adenine dinucleotide phosphate was not appreciably inhibited by treatment with either of the enzymes or by ultraviolet irradiation.Carbonylcyanide m-chlorophenylhydrazone became a potent inhibitor of electron transport after trypsin treatment of chloroplasts. It also inhibited, rather than uncoupled, electron transport in glutaraldehyde-fixed chloroplasts. No other uncouplers tested showed these effects. Glutaraldehyde fixation of chloroplasts also greatly reduced the inhibitory effects of lipase and trypsin digestion but not the inhibition by ultraviolet irradiation.The inhibitory effects of trypsin and pancreatic lipase, and probably ultraviolet irradiation as well, appear to be due to a general breakdown of the membrane structure rather than inactivation of specific sites in the electron transport chain.