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THE CONTROL OF METABOLISM BY BLUE LIGHT IN Acetabularia mediterranea—II. SELECTIVE TRANSLATIONAL CONTROL AND DIFFERENTIAL DEGRADATION OF ENZYMES
Author(s) -
Nickl Bernhard,
Söllner Bruno,
Schmid Rainer
Publication year - 1988
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1988.tb02891.x
Subject(s) - enzyme , biochemistry , uridine , acetabularia , protein biosynthesis , enzyme assay , chemistry , cytosol , specific activity , reductase , metabolism , stimulation , biophysics , biology , rna , neuroscience , gene
Abstract— During prolonged continuous irradiation with red light the specific activity of uridine 5′‐diphosphoglucose (UDPG) pyrophosphorylase (uridine 5′‐triphosphate: glucose 1‐phosphate uridylyl‐transferase EC 2.7.7.9) decreased in Acetabularia mediterranea Lamouroux (=A. acetabulum (L.) Silva). Subsequent blue light restored the original activity within a comparatively short period of 3 to 4 days. Computer‐aided quantitative evaluation of density labelling experiments showed that the synthesis of the enzyme was accelerated about four‐fold during the period of activation by blue light. A similar increase in the rate of synthesis was found for hydroxypyruvate reductase (EC 1.1.1.81), a control enzyme that showed no blue light‐dependent changes in the specific activity under these conditions. The increase in the rate of enzyme synthesis was caused by an overall stimulation of the cytosolic translation. Degradation of UDPG pyrophosphorylase was unaffected by blue light, while the half life of hydroxypyruvate reductase was shortened about two‐fold compared to continuous red light. Thus, degradation of proteins appears to be selectively light dependent in Acetabularia. Model calculations for enzyme amount and enzyme synthesis were carried out using the measurements of enzyme activity, rates of cytosolic protein synthesis, and degradation constants of the enzymes. Assuming that activities represented amounts of the given enzymes, these calculations indicated a selective activation of UDPG pyrophosphorylase synthesis by blue light since it did not coincide with the overall stimulation of protein synthesis in the cytosol, in contrast to hydroxypyruvate reductase.