A developmentally controlled change in the post-translational modifications on the lysosomal alpha-mannosidase of the cellular slime mould Dictyostelium discoideum.
During the development of the cellular slime mould Dictyostelium discoideum, a second form of a number of lysosomal enzymes begins to accumulate. The second ('late') form of these enzymes differs from the pre-existing ('early') form in post-translational modification. Pulse-chase experiments using [35S]methionine show that the late form of alpha-mannosidase-1 is made by synthesis de novo starting 8 h after the onset of development. These experiments show there is no interconversion between early and late forms in vivo. A one-dimensional peptide map indicated that the early and late forms of alpha-mannosidase have similar amino acid sequences. The two forms have a similar half-life in vivo when measured during the same period of development. Double-labelling studies were performed with 35SO4 and [3H]leucine or 32PO4 and [3H]leucine. and these studies indicated that the oligosaccharides present on the early form of alpha-mannosidase contained more sulphate and phosphate than did those on the late form. The early enzyme had a 10-fold higher 35S/3H ratio and a 4-fold higher 32P/3H ratio. Endocytosis experiments using early and late alpha-mannoside showed that the early form was efficiently taken up by human fibroblasts, whereas the late form was poorly endocytosed. This suggests that the late form lacks the mannose 6-phosphate residue required for efficient uptake.
Moore
B R
BR
Department of Biological Sciences, State University of New York, Buffalo 14260.
Vladutiu
G
G
Free
S J
SJ
D002846:Chromatography, Affinity; D004023:Dictyostelium / Q000201:enzymology*; D004591:Electrophoresis, Polyacrylamide Gel; D004705:Endocytosis; D008247:Lysosomes / Q000201:enzymology; D008361:Mannosidases / Q000378:metabolism*; D010446:Peptide Fragments / Q000032:analysis; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D043323:alpha-Mannosidase
D010446:Peptide Fragments; D008361:Mannosidases; D043323:alpha-Mannosidase