Organ distribution of rat kynureninase and changes of its activity during development

Kynureninase activity was measured in various organs of the rat by a sensitive assay method based on the use of an HPLC system. High activities were detected in liver, kidney and spleen, and much lower activities in adrenals, intestine, lung, heart, brain, skeletal muscle and pancreas. Kynureninase of liver, kidney and spleen showed the same molecular weight (110,000) and the same isoelectric point (pI 5.4). They also showed the same properties of heat stability and apparent optimum pH. The enzymes in kidney and spleen were localized in the cytosol. The developmental study showed increasing activities of the enzyme after birth and a maximum on the 60th day in both liver and spleen. The activity in kidney increased after birth and reached a plateau on the 30th day.