Alteration of the substrate specificity of 3-oxo- Delta super(5)-steroid isomerase by mutation of the catalytic base (Asp-38 to Glu-38)

We report that mutation of Asp-38 to Glu-38 in 3-oxo Delta super(5)-steroid isomerase alters the enzyme specificity, decreasing k sub(cat) 300-fold toward 5-androstene-3,17-dione but only 32-fold toward 5-pregnene-3,20-dione. This 10-fold difference in specificity is due to a modification of the catalytic base of the enzyme (Asp-38) rather than any change in the amino acids involved in binding.