Some observations on the deamination of deoxynucleotides and deoxynucleosides by normal rat liver and hepatomas.

Deamination of deoxycytidylate, deoxyguanylate, and deoxyadenylate, as well as deoxyadenosine and deoxyguanosine, by rat liver and several hepatomas was studied by a method based on the determination by a Conway diffusion technic of the am monia formed. Several factors affecting the enzyme reactions were considered, and the application of the method to the estimation of deaminase activity in tissues with low activity was demonstrated. By this technic it was shown that normal rat liver had a deoxycytidylate deaminase activity of 46 j@moles deaminated/gm protein/hr. Dunning hepatoma consistently exhibited half this activity, whereas the activity of Reuber and a number of sublines of Morris 5123 tumor were in the normal range. Extremely high activities were found in the McCoy MDAB and Novikoff hepatomas, in confirmation of previous reports. The deamination of deoxyadenylate and deoxyguanylate by tumor and normal tissues was considerable, but, since the activity measured may be the resultant of the combined action of as many as three enzymes, the relationship of purine deoxynucleo tide deamination to hepatoma growth cannot be determined until the enzymes are separated. The deamination of deoxyadenosine and deoxyguanosine, on the other hand, is less equivocal, and it was observed that these enzyme activities varied greatly in different hepatomas when compared with normal liver. Because of this and the large differences in deoxycytidylate deaminase activities, it was suggested that each hepatoma may have a unique pattern of deoxynucleotide metabolism.