Search PubMed⌕ Search

Biomedical subjects

D A Usher

Publications and source records attributed to D A Usher.

23 records · Page 2Linked to original sources
PubMed1969

On the mechanism of ribonuclease action.

All the suggestions that have been made for the mechanism of action of ribonuclease can be classified into one or another of two classes, depending on the geometry of the displacement in the first step. Studies of related model compounds indicate that one of these two classes should include as a part of the mechanism a pentacoordinate intermediate, which undergoes pseudorotation before product can be formed. It is unlikely that the pseudorotation would be rate-limiting in the reaction of the normal substrate.

Chemical Phenomena↗
PubMed1969

The hydrolysis of uridine cyclic phosphonate catalyzed by ribonuclease-A: implications for the mechanism of action of the enzyme.

Uridine 2',3'-cyclic phosphonate (I) is slowly hydrolyzed by ribonuclease-A with k(2) and K(m) values at pH6 that are respectively 1900 and 15 times smaller than the same parameters at the same pH for the related phosphate (II). Since the ratio of rate constants for hydroxide ion catalyzed hydrolysis is about 4, this result is consistent with, but does not prove a mechanism for the enzymic reaction that requires a pseudorotation.

Kinetics↗