The cell-free extract of Mucor javanicus was capable of riboflavinylglucoside formation from riboflavin and maltose. Two peaks of the riboflavinylglucoside producing activity were observed in 0.6 and 0.9 ammonium sulfate saturation fractions of the cell-free extract. The optimum pH of the former fraction was 4.5,and of the latter was 4.0. The substrate specificities of these two fractions were not coincident.
