Some properties of a lipase from Rhizopus arrhizus separation of a glycopeptide bound to the enzyme

Abstract

The exocellular lipase from Rhizopus arrhizus is a glycoprotein of molecular weight around 43 000, containing 13–14 molecules of mannose and 2 molecules of hexosamine and a single N-terminal aspartic acid residue (or asparagine). This lipase (lipase I) consists of 2 apparently noncovalently linked portions: a glycopeptide of molecular weight around 8500 and the enzyme protein. This latter can be easily freed from the glycoprotein by heating or by precipitation in the cold with 5% trichloroacetic acid. The glycopeptide does not play any role in the catalytic function of the enzyme. Upon long storage of lipase I, this glycopeptide separates and lipase I is converted into a second active form, lipase II. This slow separation is paralleled by a fragmentation of the glycopeptide into peptides and shorter glycopeptides. The enzymic protein also seems to be partly degraded as shown by the disappearance of the single N-terminal aspartic acid (or asparagine) residue and the appearance of several other N-terminal residues in non-stoichiometric proportions.