Different Molecular Forms of Invertase in the slime Variant of Neuospora crassa: Comparison with the Wild-type Strain

SUMMARY: Invertase synthesis, regulation and secretion in the wall-less slime variant of Neurospora crassa was studied. Unlike the wild-type, synthesis of the enzyme was not repressed by glucose. This effect was not related to the os mutation harboured by the slime strain, nor to the phenotypic absence of a cell wall. Three molecular forms of extracellular invertase, which varied in size, were detected in the slime strain. These forms were interconvertible, with the equilibrium in favour of the larger form. Polypeptide analysis of the three separated forms revealed that all contained the same glycoprotein with an M r of 97000. This was completely deglycosylated by treatment with endo-β-N-acetylglucosaminidase H (Endo H) to a polypeptide with an M r of 72000. It was concluded that the three interconvertible forms correspond to the monomeric, dimeric and tetrameric states of the enzyme. Three similar forms of invertase, albeit of slightly different electrophoretic mobility, were found in cell-free extracts, cell walls and spent culture medium of the wild-type strain. After Endo H treatment, analysis showed that these forms contained a polypeptide that was equally reactive against anti-Saccharomyces cerevisiae antibodies, and had the same M r, as the polypeptide produced by the slime strain.