Detection and partial characterization of activity of chlorophyll synthetase in etioplast membranes.

TLDR: The esterification of chlorophyllide a was investigated an irradiated etioplast-membrane fractions from oat seedlings and a new chlorphyll esterified with farnesol was detected which does not occur in intact plants.

Abstract: The esterification of chlorophyllide a was investigated in irradiated etioplast-membrane fractions (‘broken etioplasts’) from oat seedlings (Avena sativa L.). As a substrate, [1-3H]geranylgeraniol and its monophosphate and diphosphate derivatives were prepared by chemical synthesis. Geranylgeraniol and its monophosphate derivative are incorporated into chlorophyll only in the presence of ATP whereas the diphosphate derivative is incorporated also without ATP. The yield of esterified chlorophyll is 80–90% of chlorophyllide with saturating substrate concentrations. The term ‘chlorophyll synthetase’ is used to describe this enzyme activity which is different from chlorophyllase. Other substrates are phytol and farnesol either with ATP or as the diphosphate derivatives. The relative specificity of ‘chlorophyll synthetase’ for these substrates is geranylgeraniol: phytol: farnesol = 6:3:1. In these experiments in vitro, a new chlorophyll esterified with farnesol was detected which does not occur in intact plants. Geraniol and n-pentadecanol are no substrates for the enzyme. Proto-chlorophyllide which is present in non-irradiated etioplast membrane fractions is not esterified under the same conditions.