Biosynthesis of secreted beta-hexosaminidase in Tetrahymena thermophila. A comparison of the wild type with a secretory mutant.
The synthesis and secretion of beta-hexosaminidase was studied in wild type and secretion-deficient Tetrahymena thermophila cells by metabolic labelling and immunoprecipitation. beta-Hexosaminidase is synthesized as a Mr 79,000 polypeptide which is within 10 min converted into a Mr 59,000 form. The Mr 59,000 polypeptide is further processed (within 20 min) into at least three major mature forms of Mr 58,000-54,000, which are almost quantitatively secreted into the culture medium within 1-2 h after their synthesis. Both precursor and mature forms contain asparagine-linked oligosaccharide chains which are cleavable by endoglucosaminidase F, but not by endoglucosaminidase H. Neither [32P]orthophosphate nor [35S]sulphate are incorporated into immunoprecipitable precursor and mature beta-hexosaminidases, suggesting the absence of a phosphorylated recognition marker. Biosynthesis and processing of beta-hexosaminidase is apparently unaltered in the secretory mutant MS-1; however the processed polypeptides remain cellular bound in the mutant, indicating that the mutation affects a late event in the secretion pathway of lysosomal enzymes.
Hünseler
P
P
Zoologisches Institut der Westfälischen Wilhelms-Universität, Münster, Federal Republic of Germany.
Tiedtke
A
A
von Figura
K
K
D000818:Animals; D002478:Cells, Cultured; D011232:Chemical Precipitation; D004591:Electrophoresis, Polyacrylamide Gel; D009154:Mutation; D009844:Oligosaccharides / Q000032:analysis; D010446:Peptide Fragments / Q000032:analysis; D010455:Peptides / Q000378:metabolism; D013768:Tetrahymena / Q000201:enzymology* / Q000235:genetics; D001619:beta-N-Acetylhexosaminidases / Q000096:biosynthesis* / Q000276:immunology
D009844:Oligosaccharides; D010446:Peptide Fragments; D010455:Peptides; D001619:beta-N-Acetylhexosaminidases