On the specific binding of protochlorophyllide and chlorophyll to different peptide chains.

By means of labelling experiments with δ-[(3)H]aminolevulinic acid (ALA) and SDS acrylamide gel electrophoresis the following results were obtained with plantlets of Zea mays L.: Protochlorophyllide is associated with two peptide chains of the molecular weights (MW) 21000 and 29000, thus forming two protochlorophyllide holochromes. Chlorophyll may be associated with four peptide chains of MW 21000, 25000, 29000 and 70000, forming four chlorophyll holochromes. When plantlets are transfrrred to light, protochlorophyllide is converted to chlorophyll but this remains associated with the peptide chains MW 21000 and 29000; in addition, chlorophyll is synthesized from unmetabolized ALA and associated with peptide chains MW 25000 and 70000. These conversions occur both in dark-grown plantlets and in green plantlets transferred to darkness and then again exposed to light, but in the latter considerably faster than in the former. The results suggest the existence of two pathways for the formation of chlorophyll holochromes, one requiring a dark period followed by light, the other occurring without a dark phase. Light may not only be required for photoconversion of protochlorophyllide to chlorophyll, but may also be involved in the regulation of the formation of the protein-pigment complexes.