Light dark modulation of glycogen phosphorylase activity in the blue‐green alga, Anacystis nidulans

Abstract

Abstract The photoautotrophic procaryote, Anacystis nidulans, accumulates glycogen as a carbon reserve during illumination and nitrogen limitation. Glycogen phosphorylase participates in the mobilization of the polysaccharide in a dark period and was found to be a point of regulatory control of glycogen degradation. Specific enzyme activity of non‐dividing cells increased twofold upon transfer from light to dark and decreased again upon re‐illumination. This dark stimulation of enzyme activity was not inhibited by either rifampicin or chloramphenicol, whereas a light‐induced decrease was abolished by DCMU, an inhibitor of photosynthetic electron transport. Deactivation of glycogen phosphorylase could be simulated by dithiothreitol in vitro. A spheroplast lysate either with or without chromatophores and a partially purified glycogen‐enzyme complex responded to dithiothreitol.These results are compatible with an interpretation in terms of redox changes taking place with the enzyme in an activation/deactivation cycle. The inactive form maintained in a reduced state by photosynthetic electron transport is thought to be converted into an active form in the dark.