Isoenzymes of Lactate Dehydrogenase in Swine Stability During Storage at Different Temperatures and By Heat Treatment

The isoenzymes of lactate dehydrogenase (LDH) in serum from normal pigs were studied after separation by agar gel electrophoresis with subsequent staining with a tetrazolium salt. Experiment 1. The stability of isoenzymes was investigated for 5 successive days after storage at room temperature (22°C), in the refrigerator (4°G), and once after storage for 32 days in the deep-freezer (—20°C). Greatest loss of activity was seen after storage in the refrigerator, where LDH2 and LDH3 lost most of its activity after 5 days. In LDH4 and LDH5 no loss had occurred at this time. Also at room temperature great losses were seen in LDH2 and LDH3. After storage in the deep-freezer an increase in LDH3 activity was recorded. Experiment 2. Serum samples were kept in water baths for 30 min. at 50, 53, and 56°C. A simultaneous and increasing loss in activity of LDH3, LDH4, and LDH5 was seen from 50° to 56°C. At 56° no activity was left in LDH3, LDH4, or LDH5, and only about 15 % of the original activity was present in LDH2. LDH1 showed no loss at 56°, but all activity was lost at 65°. A close correlation was found between total lactate dehydrogenase and α-hydroxybutyrate dehydrogenase activity in both experiments.