The effect ofuncouplers (F)CCCP and NH4Cl on the kinetics of the flash-induced P515 electrochromic bandshift in spinach chloroplasts

The effect of uncouplers of photophosphorylation on the kinetics of the flash-induced P515 electrochromic bandshift was investigated in dark-adapted chloroplasts. It was found that the presence of low concentrations of carbonyl cyanide p -trifluoromethoxyphenylhydrazone (FCCP) and carbonyl cyanide m -chloro-phenylhydrazone (CCCP) resulted in the selective suppression of the slow P515 absorbance change (reaction 2), whereas the fast change (reaction 1) was not influenced. In contrast, high concentrations of NH 4 Cl did not alter the P515 response with respect to reactions 1 and 2. These results indicate that reaction 2 is specifically sensitive towards uncouplers which exert their function as a proton carrier in the lipophilic phase of the membrane.