Changes in lactate dehydrogenase enzyme pattern in Chinese hamster cells infected and transformed with Simian virus 40.

The lactate dehydrogenase (LDH) isozyme patterns of consecutive passages of Chinese hamster embryo cultures were monitored. At early passages the population displayed two LDH bands, M4 and M3H; however, at higher passages the cultures exhibited M2H2, M2H, and M4. When primary cultures of Chinese hamster embryo cells were infected with simian virus 40 (SV40), no change in the LDH pattern was observed; however, the total activity of LDH increased. Twenty-three of 25 transformed colonies isolated from SV40-infected primary cells by their ability to grow in methyl cellulose produced only M4 or M4-M3H isozymes bands. Four of the SV40-transformed clones that produced only the M4 isozyme were tested for LDH activity and found to have activities 2.5 to 3 times greater than the control cells. Chinese hamster kidney epithelial cells transformed with SV40 virus had a decrease in the H subunit production, from 57 to 31%, compared with normal kidney epithelial cells. This decrease in H subunit production led to an increase in the cathode-migrating isozymes. Therefore, a shift to the cathode-migrating isozyme was observed in SV40-transformed cells. This change in LDH pattern might represent a reversion to the enzyme pattern present in fetal cells.