Activities of several enzymes in serum and heparinized plasma from rats

The activities of lactic dehydrogenase, malic dehydrogenase, aspartate aminotransf erase, fructose-1,6-diphosphate aldolase and isocitric dehydrogenase were higher in serum from rat blood that had clotted at room temperature for 1 h than in serum separated from blood immediately. During clotting, the activities of alanine aminotransferase, sorbitol dehydrogenase, glutamic dehydrogenase, fructose-1-phosphate aldolase and ornithine carbamyl transferase did not increase. When blood was heparinized and stored at room temperature for l or 2 h, with the exception of lactate dehydrogenase the activities of these enzymes in the plasma prepared from that blood did not increase with time.Phosphate buffer was used in all but the ornithine carbamyl transferase assay. Tris-HCl or triethanolamine buffers were unsuitable because when they were used the assay mixtures became opaque when some of the heparinized samples were analyzed. In the supernatant fraction from sonicated blood, activities over 10 mU/ml were obtained for lactic dehydrogenase, malic dehydrogenase, aspartate aminotransferase, fructose-1,6- diphosphate aldolase, alanine aminotransferase and sorbitol dehydrogenase.