THE CONTROL OF METABOLISM BY BLUE LIGHT IN Acetabularia mediterranea—I. LIGHT DEPENDENCY AND EVIDENCE FOR POST‐TRANSCRIPTIONAL CONTROL OF UDPG PYROPHOSPHORYLASE AND PYRUVATE KINASE

Abstract

Abstract— After a preculture in white light, Acetabularia mediterranea Lamouroux (=A. acetabulum (L.) Silva) was irradiated with either continuous red or blue light. In crude extracts, the specific activities of UDPG pyrophosphorylase(uridine–5′‐triphosphate: glucose 1‐phosphate uridylyltransfer‐ase EC 2.7.7.9) and pyruvate kinase(adenosine–5′‐triphosphate: pyruvate phosphotransferase EC 2.7.1.40) varied as a result of the different light qualities. In red light activities decreased to 40% and 60%, respectively, within 3 weeks of irradiation, while under blue light, if not preceded by a red irradiation, the activities remained unchanged. After prolonged red light, high enzyme activities were restored by blue light with a relatively rapid time course (3 to 4 days for completion) compared with the decrease in red light. A fluence‐response curve for the activation of UDPG pyrophosphorylase showed two phases with different sensitivities for blue light.The blue light‐mediated increase in the activities of both enzymes was unaffected when the cell nucleus was removed before the beginning of the blue irradiation. The increase was inhibited by cycloheximide but not by chloramphenicol. Thus, functional cytosolic translation but not de novo transcription products are presumed to be required for the increase in specific enzyme activities in vivo.