172 BIOCHIMICA ET BIOPHYSICA ACTA BB,lk 96~36 APPARENT CHANGES IN MOUSE LIVER DNA CONTENT DUE TO INTERFERENCE BY NON-DNA DIPHENYLAMINE-REACTING CYTOPLASMIC MATERIAL MARVIN EDELMAN*, CARL A. HIRSCH, HOWARD H. HIATT ANn MAURICE FOX Departments o[ Medicine, Harvard Medical School and the Beth Israel Hospital, Boston, Mass. 02215, and Department o[ Biology, Massachusetts Institute o[ Technology, Cambridge, Mass. o2r39 (U.S.A.) (Received August 3oth, 1968) (Revised manuscript received November i5th , 1968) SUMMARY A significant decrease occurs in the amount of diphenylamine-reacting material extracted with a nucleic acid fraction of liver if rats or mice are deprived of food for several days. However, this decrease, which is rapidly regained on refeeding the animals, does not represent loss of liver DNA, for no corresponding decrease was found if DNA was assayed by phosphate content or ultraviolet absorbance. The interfering material, which is predominantly cytoplasmic, yields a colored product in the diphenylamine reaction, resembling that given by deoxyribose but having an absorbance maximum at about 660 m/z rather than at 600 m/~. Also, the rate of color development with the interfering substance is slower than that observed with deoxy- ribose. INTRODUCTION During a study of ribosome turnover, an apparent reduction in total DNA, as measured by the diphenylamine assay, was observed consistently in the livers of rats fasted for several days 1. Although a previous investigation had not detected such an effect of fasting 2, reports that the DNA content per cell can fluctuate in response to cortisone administration in the case of rat liver 3,4, and to stress to the animal in the case of rat adrenal medulla 5,n, as well as evidence for a metabolically active component of mouse liver DNA 7-0, led us to investigate further the apparent diminution in liver DNA content that we had observed. The evidence presented in this report indicates that this diminution results from loss not of DNA but of some other diphenylamine- reacting constituent. MATERIALS AND METHODS Animals Mice were used in these experiments since it was found that their response to fasting was similar to that of rats, but more rapid. Two strains were used, C-57 (Jack- * Present address: Department of Biochemistry, Weizmann Institute of Science, Rehovoth, Israel. Biochim. Biophys. Acta, i79 (I969) I72-I78