Localization of Phosphate-Independent Glutaminase in the Brush Border of Rat Kidney Cortex

Abstract

A microsomal fraction that contains the highly enriched activities of NADPH – cytochrome c reductase, 5′-nucleotidase, phosphate-independent glutaminase, and alkaline phosphatase was isolated by differential centrifugation from rat kidney cortex. Continuous sucrose density gradient studies on this fraction have shown that the distribution pattern of phosphate-independent glutaminase is identical with that of alkaline phosphatase and the specific activity of these enzymes in peak fractions were 13- to 17-fold higher than in the whole homogenate. These results indicate that the phosphate-independent glutaminase is localized in the brush border of rat kidney cortex. The enzyme is truly membranous as it could not be removed by sonication, salt treatment, or pH alterations.