Human pancreatic ribonuclease presents higher endonucleolytic activity than ribonuclease A

Analyzing the pattern of oligonucleotide formation induced by HP-RNase cleavage shows that the enzyme does not act randomly and follows a more endonucleolytic pattern when compared to RNase A. The enzyme prefers the binding and cleavage of longer substrate molecules, especially when the phosphodiester bond that is broken is 8–11 nucleotides away from at least one of the ends of the substrate molecule. This more endonucleolytic pattern is more appropriate for an enzyme with a regulatory role. Deleting two positive charges on the N-terminus (Arg4 and Lys6) modifies this pattern of external/internal phosphodiester bond cleavage preference, and produces a more exonucleolytic enzyme. These residues may reinforce the strength of a non-catalytic secondary phosphate binding (p2) or, alternatively, constitute a new non-catalytic phosphate binding subsite (p3).