The Role of Lysine-7 in Ribonuclease-A
Bovine pancreatic ribonuclease A(RNase A) catalyzes the hydrolysis of RNA by a two-stage mechanism. The first step is a transphosphorylation to give an oligonucleotide terminating in a pyrimidine 2′-3′-cyclic phosphate. The second is the hydrolysis of the cyclic phosphate to give a terminal 3′-phosphate. At present it is not clear whether the invariant lysine-7 plays any part in the enzyme activity. Chemical modifications of the ε-ammonium group give derivatives with 15–30% activity, but substrate binding has been observed to be unaffected. On the other hand, the X-ray crystallography data, while confirming that Lys-7 is located relatively close to and with free access to the active site, strongly suggest that this residue is still too far away from the site to interact with the substrate (1).
KeywordsHydrolysis Titration Pyrimidine Borin
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