Microheterogeneity in yeast invertase.
Yeast external invertase (EC 3.2.1.25), a glycoenzyme consisting of equal parts by weight of protein and mannan, has been found to contain covalently bound phosphate. Three preparations (from two yeast strains) had mannose/PO4 ratios of 31-35, equivalent to 24-27 PO4 residues per mol of enzyme, while a fourth had only 7 PO4 residues per mol. From one of the high-PO4 enzymes, approx. 69% of the phosphorus was recovered as mannose 6-phosphate. No correlation was found between invertase activity and phosphorus content. The PO4 contents of the invertases exceeded those of the cell wall mannans from the respective yeasts. Thus, contamination of the invertases by cell wall phosphomannan is unlikely. Electrofocusing of the low-PO4 invertase yielded four components with pI values from 3.96 to 4.40, and yeast internal invertase (a mannan- and PO4-free, cytoplasmic isozyme) was isoelectric at approx. pH 4.5. The high-PO4 invertase was considerably more heterogeneous, with two major species of pI 3.65 and 3.32 and a highly acidic component of pI smaller than 2.7; however, the mannose/PO4 ratio of each species was approximately the same. PO4-gradient elution from hydroxyapatite resolved the high-PO4 invertase into five isozymes of increasing acidity and mannan content. Since the mannose/PO4 ratios of these invertase species are constant, the increase in the mannan/protein (and, therefore PO4/protein ratio is apparently responsible for the microheterogeneity of phosphoinvertase.23
D002845:Chromatography; D006023:Glycoproteins / Q000032:analysis; D006600:Hexosephosphates / Q000032:analysis; D006882:Hydroxyapatites; D007525:Isoelectric Focusing; D007527:Isoenzymes / Q000032:analysis; D008358:Mannose / Q000032:analysis; D009943:Organophosphorus Compounds / Q000032:analysis; D010750:Phosphoproteins / Q000032:analysis; D012440:Saccharomyces / Q000201:enzymology*; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013045:Species Specificity; D013393:Sucrase / Q000032:analysis
D006023:Glycoproteins; D006600:Hexosephosphates; D006882:Hydroxyapatites; D007527:Isoenzymes; D009943:Organophosphorus Compounds; D010750:Phosphoproteins; D013393:Sucrase; D008358:Mannose