Specific Requirements for the Action of Deoxyribonuclease

Abstract

THE mechanism of action of pancreatic deoxyribonuclease, now available in the crystalline state^1,2, on highly polymerized deoxypentose nucleic acids is still obscure. The enzymatic attack is known to result in the formation of dialysable oligonucleotides and of a non-dialysable ‘core’ which, in the case of the nucleic acids from calf thymus^3,4 and wheat germ⁵, is characterized by proportions of adenine, and to a lesser degree of thymine, greatly in excess of those encountered in the original substrate. Mononucleotides and inorganic phosphate are not found among the degradation products^3,4, and this precludes the attribution to deoxyribonuclease of functions similar to those of phosphomonoesterases. It could be regarded as a phosphodiesterase of a closely circumscribed, as yet undefinable, specificity. A small number of acidic groups is, in fact, Liberated during the digestion⁶. That the attack of an enzyme the action of which consists in the depolymerization of a substance of high molecular weight, exhibiting no easily recognizable periodicity of constituent sequence, must follow an intricate pattern is clear: every break of the original molecule produces substrates that are new and different; the enzyme must deal with kaleidoscopic substrate changes.