The Reduction of Protochlorophyllide into Chlorophyllide

The temperature dependence of the P657-647 to P688-676 phototransformation in etiolated bean leaves was studied using either 647 or 630 nm actinic light. When irradiating with 647 nm photons the photoransformation rate increased from +37 °C to -18 °C; the rate decreased below -18 °C; it became zero at about -75 °C. When irradiating with 630 nm photons one of the two first-order rate constants of the phototransformation behaved similarly to the rate constant found in the presence of 647 nm photons; the other 630 nm rate constant behaved in another way. Denaturation of the protochlorophyllide-lipoprotein complex occurred in the dark at temperatures higher than +45 °C. A strong decrease of the phototransformation rate was found at these temperatures.