Molecular and Cellular Biochemistry 66, 45-53 (1985). © 1985, Martinus Nijhoff Publishers, Boston. Printed in the Netherlands. Differential expression of multiple forms of arginase in cultured cells a Elaine B. Spector, Rita M. Kern, Donald F. Haggerty and Stephen D. Cederbaum* Departments of Pediatrics and Psychiatry and the Mental Retardation Research Center, University of California, Los Angeles, School of Medicine, Los Angeles, CA 90024, USA Summary Arginase (EC 3.5.3.1), the final enzyme in the urea cycle, catalyzes the cleavage of arginine to orthinine and urea. At least two forms of this enzyme, AI and All, have been described and are probably encoded by discrete genetic loci. The expression of these separate genes has been studied in mammalian cells grown in culture. The permanent rat-hepatoma line H4-II-E-C3 contained exclusively the AI enzyme; the form in mammals comprising about 98% of the arginase activity in liver and erythrocytes but catalyzing only about one half of that reaction in kidney, gastrointestinal tract, and brain. By contrast, human-embryonic-kidney and -brain cells, after transformation with the human papovavirus BK, contained only the All species of arginase, which form contributes the remaining half of that catalysis in those mammalian tissues in vivo. We report here the results of an extensive study on the properties of these two forms of arginase in the three cell lines, including K m values for arginine, behavior on polyacrylamide gels under non- denaturing conditions, and cross-reactivity with lapine antibodies against the arginases from either rat or human liver. Introduction Arginase (L-arginine-urea hydrolase; EC 3.5.3.1 ) is the final enzyme in the urea cycle and catalyzes the hydrolysis of arginine to ornithine plus urea. Arginase is most abundant in mammalian liver, but is found in lesser concentrations (ca 1 to 2% of that in liver) in red blood Cells (RBC), brain, kidney, lactating mammary gland, and gastrointestinal (GI) tract (1-4). We (5, 6) and others (7-15) have described pa- tients with hyperargininemia lacking RBC-arginase activity. In two such individuals there was virtually a complete absence of arginase in the liver (6, 13); but despite this degree of hepatic-arginase deficien- cy, both of these probands retained the capacity for substantial urea production and excretion. Studies in man and rats have demonstrated that liver and kidney arginase differ from one another in both immunologic and electrophoretic properties (1, 3). The suspicion that some or all kidney argi- nase is specified by a second genetic locus was con- firmed when enzymatic activity was found to be present in the kidney of a patient with presumed liver-arginase deficiency, having undetectable lev- els of the enzyme in his RBC. Moreover, the en- zymatically active protein in the extracts from that individual was not only augmented in activity some 3-to 5-fold above average total renal values but also differed immunologically from the arginase found in normal kidney (15). From this observation and our findings with normal tissues, the totality of our serologic data have thus far suggested that the product of one gene (AI) constitutes 98% or more of a Presented in part at the annual meeting of the Society for Pedintric Research, Washingto,a, D.C., May, 1982. Pediatr. Res. 16:195A. * To whom all correspondence should be addressed.