Rapid regeneration of protochlorophyllide(650).

The rate of regeneration of protochlorophyllide(650) was examined spectrophotometrically after a saturating light flash using 8- to 9-day-old dark-grown bean leaves. The regeneration occurred to the extent of 15% with a half rise time of about 20 seconds. Feeding delta-aminolevulinic acid to the excised leaves in the dark increased protochlorophyllides(635) but not the absorption at 650 nanometers, suggesting that the holochrome was normally saturated with protochlorophyllide and that the holochrome protein was not controlled by the level of protochlorophyllide. After a light flash, the excess protochlorophyllide, formed from exogenous delta-aminolevulinic acid, readily combined to regenerate the 650 nanometer absorbing species; the regeneration occurred to the extent of 60 to 80% with a half rise time of about 50 seconds. Regeneration was blocked at 0 degrees , suggesting that there was some enzymic process required for regeneration, possibly the formation of a reductant component of the protochlorophyllides(650) holochrome.