We show an example of the importance of specifying the form of isoenzyme and source of indicator enzymes to be used in coupled enzymatic assays. When we compared H-4 (pig heart) and M-4 (rabbit muscle) isoenzymes of lactate dehydrogenase for their suitability as indicator enzymes in the assay for alanine aminotransferase activity, we found that about fourfold as much M-4 as H-4 was required in ...

The expression of alanine aminotransferase (EC 2.6.1.2), an enzyme that is inducible in the liver, has been examined in somatic hybrid cells formed by crossing well-differentiated rat hepatoma cells with rat diploid epithelial cells, the former characterized by high activity and inducibility of the enzyme, and the latter by the absence of detectable activity. The hybrid cells that contain essen...