Yeast Mannosyl Transferases Requiring Dolichyl Phosphate and Dolichyl Phosphate Mannose as Substrate

Partial Purification and Characterization of the Solubilized Enzyme

Authors

  • Peter BABCZINSKI,

    1. Fakultät für Biologie und Vorklinische Medizin, Universität Regensburg, Universitätsstraße 31, D-8400 Regensburg, Federal Republic of Germany
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  • Anton HASELBECK,

    1. Fakultät für Biologie und Vorklinische Medizin, Universität Regensburg, Universitätsstraße 31, D-8400 Regensburg, Federal Republic of Germany
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  • Widmar TANNER

    1. Fakultät für Biologie und Vorklinische Medizin, Universität Regensburg, Universitätsstraße 31, D-8400 Regensburg, Federal Republic of Germany
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Abstract

The first mannosyl unit of manno-oligosaccharides of fungal mannoproteins is transferred in a dolichyl-phosphate-dependent reaction sequence to serine/threonine residues of the protein. The two membrane-bound enzymes catalyzing this transfer in the yeast Saccharomyces cerevisiae have been solubilized by detergents. The enzyme transferring mannose from guanosine diphosphate mannose to dolichyl phosphate has been purified 18-fold when based on membrane protein and 140-fold when based on total cell protein. The enzyme transferring mannose from dolichyl phosphate mannose to protein has been purified 48-fold and 380-fold, respectively. A HCl-treated cell-wall mannoprotein from yeast served as acceptor protein for the second enzyme.

The solubilized enzyme catalyzing the formation of dolichyl diphosphate mannose has a Km for guanosine diphosphate mannose of 7 × 10−6 M and is saturated with about 0.15 mM yeast dolichyl phosphate. The metal requirement, pH-optima, and the detergent concentration necessary for optimal activity have been determined for both solubilized enzymes.

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