Constraints in the Determination of Active-Centre Topography

Abstract

THE inactivation of succinic semialdehyde dehydrogenase by trypsin has recently been found to be accelerated by a factor of greater than 100 when triphosphopyridine nucleotide, a substrate of the dehydrogenase, is included in the reaction mixture¹. Evidence was presented that the site at which triphosphopyridine nucleotide is effective is the same for both dehydrogenase activity and for acceleration of inactivation by trypsin. It was concluded that the binding of a pyridine nucleotide substrate to succinic semialdehyde dehydrogenase produces a configurational change in the enzyme, and, in so doing, results in the exposure of a linkage labile to trypsin. Indirect evidence of such configurational changes has been noted by others^2–4 and suggests that the phenomenon may be of widespread occurrence.