Abstract
Spermine stimulated the hydrolysis of 2', 3'-cyclic phosphates of cytidine and uridine by bovine pancreatic RNase A, the degree of stimulation being considerably greater with the former substrate. Similar effects of spermine were obtained with benzyl esters of 3'-cytidylic acid and 3'-uridylic acid as substrates. The degree of stimulation by spermine of the breakdown of poly (C) decreased with decrease in the molecular weight of poly (C), while the degradation of poly (U) was not influenced significantly by spermine in the molecular weight range of poly (U) from 30000 to 85000. Kinetic studies showed that polyamines did not significantly change the apparent Km of the enzyme for any substrate tested, but increased the maximal velocity of the reaction when stimulation was observed. Monovalent cations (NH4+ and K+) had stimulatory effects similar to those of polyamines on RNase A activity towards cyclic nucleotides and polynucleotides.
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