Aminotransferases

Excerpt

Aminotransferases catalyze the redistribution of nitrogen between amino acids and corresponding oxoacids participating in both protein metabolism and gluconeogenesis. They are ubiquitous in their cellular distribution.

Tissue activity for AST is as follows in decreasing concentration: heart, liver, skeletal muscle, kidney, pancreas, spleen, lung, and erythrocyte. Two distinct forms have been identified: a cytoplasmic, or soluble isoenzyme, and a mitochondrial isoform. Selective measurement of these isoenzymes has no currently demonstrated clinical application.

The distribution and relative tissue concentration of ALT is similar but importantly different. Highest activity is found in the liver, followed by kidney, myocardium, skeletal muscle, pancreas, spleen, lung, and erythrocyte. ALT activity is found in the cytosol; organ- or organelle-specific isoenzymes have not been demonstrated. The concentration of ALT in hepatic cell cytoplasm is comparable to AST; however, a mitochondrial ALT isoform is not found. In all other tissues, ALT activity is significantly less than AST.