Abstract
PANCREATIC ribonuclease catalyses the decomposition of a ribonucleic acid by a two-step mechanism: a transesterification followed by hydrolysis of the resulting cyclic phosphate1. The various mechanisms suggested can be classified as either “in-line” or “adjacent” depending on the relative geometry of the incoming and outgoing groups during the displacement reaction2 (Fig. 1). In particular, any simple mechanism in which it is assumed that the same group acts first as a general base toward the attacking nucleophile, then as a general acid toward the leaving group, implies an adjacent geometry. The alternative, in which there is a considerable movement of either the catalytic group or the substrate, is unlikely. The two steps may, however, have different mechanisms according to this criterion without violating microscopic reversibility, for a nucleoside is obviously not necessarily equivalent to a water molecule3.
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USHER, D., RICHARDSON, D. & ECKSTEIN, F. Absolute Stereochemistry of the Second Step of Ribonuclease Action. Nature 228, 663–665 (1970). https://doi.org/10.1038/228663a0
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DOI: https://doi.org/10.1038/228663a0
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