Photo-inactivation of system II centers by carbonyl cyanide m-chlorophenylhydrazone in Chlorella pyrenoidosa.

In the presence of a high concentration of carbonyl cyanide m-chlorophenylhydrazone (CCCP) (4-10(-6) M), the S2 and S3 dark decays are accelerated and become biphasic with a first half-time of 0.6 s. The first fast phase of the decays does not correspond to a simple reduction of S2, S3 back to S0, S1 (i.e. to an acceleration of the deactivation reaction), but to a decrease in the number of oxygen-evolving System II centers. This photo-inactivation produced by CCCP is rapidly reversible in the dark.