Function of Ribonuclease in Germinating Peas

Abstract

ALTHOUGH ribonucleases have been found in a large variety of tissues of plant, animal and microbial origin, only the crystalline enzyme from bovine pancreas has been studied in detail. This enzyme is known to bring about the degradation of ribonuclease by transesterification. In this process, a 5′-phosphoester residue is split and a new 2′-phosphate ester linkage is formed, giving a 2′,3′-cyclic phosphate of a pyrimidine nucleoside as shown (I→II; R ₁ = cytosine or uracil ; R ₂ = adenine, guanine, cytosine or uracil); subsequent hydrolysis of the cyclic phosphate by the enzyme then produces the 3′-hydrogen phosphate of the pyrimidine nucleoside (III)¹. Synthesis of internucleotide linkages has been demonstrated with certain ribonucleases^2,3 by reversal of the above reaction (II→I), and it has been shown that the specificity of the pancreatic enzyme in the reverse reaction is such that only linkages of the type known to be present in ribonucleic acid are formed⁴. The involvement of ribonucleases in the synthesis of ribonucleic acid has frequently been suggested; but, although the capacity of the enzyme to effect synthesis is not in doubt, it is difficult to obtain direct evidence to support the hypothesis that ribonucleases fulfil a synthetic function in the cell.