Abstract: A functionally active hyaluronan synthase having at least one modified amino acid residue therein as compared to a corresponding functionally active native hyaluronan synthase such that the functionally active hyaluronan synthase has an altered enzymatic activity as compared to the corresponding functionally active native hyaluronan synthase is disclosed. The altered enzymatic activity may result in increased or decreased activity when compared to the corresponding native hyaluronan synthase, or the altered enzymatic activity may result in production of hyaluronan having an average molecular mass that is greater than or less than an average molecular mass of hyaluronan produced by the corresponding native hyaluronan synthase. Methods of producing hyaluronic acid utilizing a recombinant host cell having an expression construct encoding the functionally active hyaluronan synthase with altered enzymatic activity are also disclosed.