Ribonuclease configurational studies

Stereochemical studies support in-line mechanisms for both the transesterification and hydrolysis steps of ribonuclease catalysis. For example, chiral uridine 2, 3 -cyclic phosphorothioates are hydrolyzed with inversion of configuration, with the diastereoisomer shown yielding a 2 -monophosphothioate of the R configuration at phosphorus. 

Among all possible configurations, the active enzyme conformation is assumed to be thermodynamically the most stable in situ. Experimental evidence to validate this assumption came from reversible denaturation studies on enzymes. For example. ribonuclease may be completely unfolded in urea solution after breakage of four native intramolecular disulphide bridges. Afterwards, when ribonuclease is brought to renature in the proper conditions, the native disulphide bonds are restored, and the protein recovers its catalytic activity. This case must be regarded, however, as a very favourable one because in most instances renaturation is... 

Slim, G. and Gait, M J (1991) Configurationally defined phosphorothioate-containing oligoribonucleotides in the study of the mechanism of cleavage of hammerhead ribozymes Nucl. Acids Res 19,1183-1188 Pieken, W A, Olsen, D. B, Benseler, F., Aurup, H, and Eckstein, F (1991) Kinetic characterization of ribonuclease-resistant 2 -modified hammerhead ribozymes. Science 252, 314-317... 

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