Spleen deoxyribonuclease

The question of enzyme specificity for irradiated polynucleotides is taken up in more detail in the recent review of Johns.11 The specificities of four enzymes, spleen phosphodiesterase, snake venom phosphodiesterase, pancreatic ribonuclease, and pancreatic deoxyribonuclease are discussed. 

Acid deoxyribonuclease (DNase) is an enzyme which splits the phosphodiester bonds of native DNA by both a diplotomic and a haplotomic mechanism (see Section 111,0) leaving the terminal phosphate in a 3 position. The enzyme is very widely distributed in animal cells and appears to be localized in the lysosomes. The best known acid DNase is that from hog spleen this explains why most of the data presented here refer to this enzyme. It should be stressed, however, that the properties of acid DNases obtained from the tissues of other vertebrates appear to be extremely similar to those of the hog spleen enzyme ... 

The enzyme has also been called spleen phosphodiesterase (1,2) and phosphodiesterase II (3). We prefer to use the term phosphodiesterase as a general name for the broad group of enzymes hydrolyzing phos-phodiester bonds whether between nucleosides or not (4). Table I gives a few examples of such enzymes. The term phosphodiesterase II (3), intended to mean an enzyme releasing nucleoside-3 -phosphates, seems to be an unhappy one, like that of deoxyribonuclease II (5) from... 

A method for the partial purification of spleen exonuclease was described by Heppel and Hilmoe in 1955 (13) and by Hilmoe in 1960 (14) this was later improved by Razzell and Khorana (15) and Richardson and Kornberg (16). In 1966, we described a novel purification procedure (10) leading to an enzyme preparation with a specific activity comparable to that of the best preparation of Razzell and Khorana (15). Enzyme yields were, however, low the method was therefore modified and satisfactory results were obtained (11). The new method involves the preparation of a crude enzyme obtained essentially as in the case of acid deoxyribonuclease (5, 17). The main differences are that acidification to pH 2.5 is avoided and (NH4)2S04 fractionation is done between 35 and 60%> saturation. The crude enzyme is then purified by chroma-... 

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