The subcellular localization of the isoenzymes of glutaminase has been studied in rat renal cortex. Differential and sucrose density centrifugation techniques demonstrated a mitochondrial localization for phosphate-dependent glutaminase. Fractionation of isolated mitochondria by digitonin and by sonication revealed a matrix localization for phosphate-dependent glutaminase, a finding in agreement with its demonstrable latency. The highest specific activity of phosphate-independent glutaminase

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... found in the microsomal fraction. This fraction was also enriched in 5'-nucleotidase (plasma membrane marker) and NADPH-cytochrome c reductase (endoplasmic reticulum marker).