[Enzymatic system transforming chlorophyllide into chlorophyll in etiolated leaves using exogenous substrates].

The substrate specificities of the enzymatic system, which transforms chlorophyllide into chlorophyll in etioplasts of whole leaves and of the chlorophyllase enzyme, which performs the inverse reaction, i. e. chlorophyll hydrolysis, were compared. Infiltration of chlorophyllide a of b into the excised etiolated leaves of rye results in a formation of chlorophylls a and b in the dark, whereas pheophorbide a or b does not cause pheophytin to appear under the same conditions. Consequently, for the in vivo esterification reaction to occur, substitution of the methyl group by the formyl one in position 3 of the tetrapyrrole ring is not essential, but the presence of the central magnesium atom in the molecule is necessary. On the other hand, chlorophyllase from the same etiolated leaves equally hydrolyzes both chlorophylls and pheophytins. It is concluded that the enzymes present in etioplasts which catalyze chlorophyllide esterification and chlorophyll hydrolysis are not identical. The optimal temperature of the in vivo esterification of exogenous chlorophyllide to chlorophyll (37 degrees) was determined and the ability of this chlorophyll to be hydrolyzed by chlorophyllase was established.