The Conversion of Citrulline to Arginine (Transimination) by Tissue Slices and Homogenates

The conversion of citrullme to arginine by a transimination reaction involving glutamic acid and metabolically related compounds has been reported to take place in kidney slices by Borsook and Dubnoff (1).These authors found that liver slices did not catalyze the reaction and further that the breakdown of cell structure of kidney tissue, such as by homogenization, resulted in a loss of activity.In the course of an investigation on the mechanism of urea synthesis in liver, some evidence for the transimination reaction was obtained in homogenates fortified with adenosine triphosphate (ATP), magnesium ions, and cytochrome c.These findings, which are reported in a separate publication (2), led to a study of the transimination reaction in kidney and other tissue homogenates.Experiments reported in this paper deal with (1) the conditions l;equired for demonstrating the transimination reaction in tissue homogenates and (2) the relative rates of this reaction in slices ati homogenates of kidney and liver. EXPERIMENTAL Preparation of TissuesSlices-Livers and kidneys of adult white rats were removed shortly after the animals had been decapitated, bled, and chilled on ice, and the slices were cut immediately thereafter.For liver studies, t,hree slices, totaling approximately 12 to 15 mg. in dry weight, were used in each flask.In kidney studies, two slices, approximately 7 to 10 mg. in dry weight, were used.Homogenate~Tiisues were removed from adult rats treated in the same manner as described above, and chilled on ice before being cut into small pieces to facilitate homogenization.Homogenization was carried out in the apparatus of Potter and Elvehjem (3).The cold homogenate, after straining through four layers of cheese-cloth, was added to Warburg flasks containing cold medium and substrates.All operations were carried out in a lo cold room to insure maintenance of low temperatures.The homogenate