Activity Distribution of Guanine Aminohydrolase in Rat Tissues

Enzyme activities are the most frequent examples of tissue components used in characterizing tissue functions; and standardization of relative enzyme activities, therefore, among tissues in health and disease has relevance of biochemical studies to particular biological problems of any kind. The bias in favor of enzymes with this regards, however, seems critical in any case of enzyme because the size of the rate units of enzymes is mostly determined by various degrees of subtleties of the reaction conditions as used by each reporter (Knox, 1976). It seems not to be exceptional in the case of guanine aminohydrolase (EC 3. 5. 4. 3) , while it exerts an important r91e in purine catabolism which not only involves interconversions between purines at the level of the monophosphates, the ribosides , and the free bases , but also gives rise to uric acid as the end product in man and other primates as well as in birds and terrestial reptiles and to allantoin in mammals other than the primates (Kimm, 1973). The enzyme has been under continuous investigation during the last several years by the authors' laboratory which has proved its isoenzymic nature (Kimm et at. , 1967: Cha et at. , 1980) , its significances in health and disease (Kimm and Lee, 1970; Kimm and Han , 1971), proposing a new colorimetric method for the determination of its activity (Park and Kimm, • Present Address: Department of Chemistry, Cnllege of Natural Sciences, Dong-A University 1976) and a staining method for it on the electrophoretic gel bed (Kimm , 1976). During this period it attracted the authors' attention that observations on activity patterns of this enzyme among tissues were so scanty and inconsistent to compare for the purpose of characterizing tissue functions pertinent to this particular enzyme, not to mention little progress made in the purification of the enzyme since the initial works (Schmidt, 1932: Kalckar, 1947) as well as in the study of its properties (Kumar et at. , 1965: Currie. , 1967: Kumar et at. , 1973) Fostered by interest in the regulation of purine catabolism, it came into the authors' consideration to undertake analyses of activities of guanine aminohydrolase distributed among tissues of rats because we thought it to be a burgeoning trial prior to any of the further investigation on this enzyme, of which clinical application, for instance, would cast a clue to pathological tissue diagnoses together with its biochemical implications regarding purine catabolis