Changes in leucine aminotransferase isozymes by viral transformation and its correlation with the isozyme changes occurring during differentiation.

The isozyme pattern of leucine aminotransferase (EC 2.6.1.6) in various cell lines and their viral-transformed derivatives were examined. The Wistar 3C rat liver cell line was found to contain only isozyme I, while its simian virus 40-transformed counterpart had isozyme III in addition to isozyme I. A spontaneously transformed late passage clone of these liver cells was also found to have acquired isozyme III. Polyoma virus-transformed baby hamster kidney cells were also found to contain a greater predominance of isozyme III than their normal untransformed counterpart. Examination of the isozymes in a cloned normal rat kidney cell line transformed by a mutant of Rous sarcoma virus which is temeprature-sensitive for transformation indicated that, in fact, such an isozyme change does correlate with transformation. When grown at 36 degrees these cells contained predominantly isozyme III; however, upon reacquiring normal morphology and lowered glucose transport activity when grown at 40 degrees, their isozyme pattern was now found to be changed and consisted predominantly of isozyme I, as is found in normal adult rat kidney tissue. Isozyme III was found to be present in neonatal kidney tissue of the rat and hamster, and its predominance in the virus-transformed normal rat and baby hamster kidney cells was interpreted as indicative of the dedifferentiation of these cells upon viral transformation. A similar change of the isozyme pattern of leucine aminotransferase in chicken embryos during their development was observed, such that in 5-day-old embryos Form III was predominant, while in the more mature differentiated chicken embryo of Day 17, Form I was predominant.