The deoxyribonuclease of rat liver in relation to the isolation of deoxyribonucleoprotein.

The deoxyribonuclease of various tissues is not only intrinsically interesting, but this enzyme must be considered in the development and application of procedures for the isolation of undegraded deoxyribonucleic acids and nucleoproteins. For this purpose it is particularly desirable to know the intracellular distribution of DNasel and to have information concerning factors which modify the enzymatic activity. The intracellular distribution of DNase has been studied (l-9) in various tissues of several animals by a number of methods, with some variation in conclusions. A part of this variation in results doubtless represents real differences in the distribution of DNase with respect to the type of tissue and the species of animal, but it seems likely that some of the variability can be attributed to artifacts which arise from transposition of the enzyme from one particulate fraction to another, a source of error which may be more serious with one method of fractionation than another. Schneider and Hogeboom (5) have reported that, in homogenates of mouse liver in 0.25 M sucrose, DNase is concentrated predominantly in mitochondria. Kuff and Schneider (8) and de Duve et al. (9) have found high specific activities of DNase in mitochondrial fractions of rat liver isolated in 0.25 M sucrose, but the latter authors have concluded that the DNase actually is contained in a special type of granule to which they have given the name lysosome. It is not known whether the distribution of DNase of rat liver is altered in the presence of calcium chloride which is added to 0.25 M sucrose to yield a homogenizing medium which is reported (10, 11) to have particular advantages for the isolation of nuclei. It is important to have this information in order to permit isolation of nuclei under conditions which will provide minimal opportunity for DNase action on the DNP. Maver and Greco (12, 13) reported that the DNase of calf spleen and