Proteolysis in Euglena gracilis. IV. Proteolytic Activities During Light-induced Chloroplast Formation in Resting Cells 1

Abstract

Summary Proteolytic activities were measured in cell-free extracts of Euglena gracilis resting cells during light-induced chloroplast formation. After 40 hours cultivation on resting medium in the dark, autolytic protein breakdown is increased 3fold and 10fold in the soluble and particulate fraction, respectively, compared with dark-grown stationary-phase cells. During 24 hours illumination of resting cells only a 1.5 fold increase is observed in soluble autolytic activity, whereas autolysis in the particulate fraction is decreased by 50 % with an intermediate maximum at 17 hours. The soluble and particulate proteolytic activities show qualitatively the same behavior with diazotized mitochondrial membrane proteins of Euglena as substrates. Carboxypeptidase and aminopeptidase activities are present in the soluble fractions; only the former increases slightly during illumination. The spectrum of proteinases does not change throughout the illumination period. There are only cysteine proteinases in the soluble, and about equal activities of cysteine and aspartic proteinases in the particulate fractions. Serine proteinases and metalloproteinases were not detected. We suggest that light is not of main importance for the regulation of total proteolytic activity of greening Euglena gracilis resting cells. The activities present at the onset of illumination appear to be sufficient for the supply of amino acids necessary to synthesize the proteins of developing chloroplasts.