Structural Features of Ring A and the Interaction of 20‐Oxosteroids with Cortisone Reductase

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Abstract
Kinetic mesurements were made using cortisone reductase and a series of substrates which differed in size, shape and electronic character in the region around C‐3 and in shape around C‐5. This was the part of the molecule most remote from the reacting 20‐oxo group.These structural changes in the substrate resulted in relatively small changes in the apparent Km and apparent V values. It is suggested that, in the enzyme · substrate complex, ring A is probably situated at an extremity of the substrate‐binding site and that there are relatively strong interactions between the enzyme and parts of the steroid other than ring A.