[Characteristics of isoenzymes of glucose-6-phosphate dehydrogenase in estrogen-dependent and estrogen-independent mammary tumors of experimental animals].

Estrogen-dependent and estrogen-independent mammary tumours were produced in experimental animals. Four isozymes of glucose 6-phosphate dehydrogenase were identified in each tumour tupe. It was found that ovariectomy and estradiol administration change selectively the activity of glucose 6-phosphate dehydrogenase I in estrogen-dependent tumours, while no effect on the enzyme or any of its isozymes was found in estrogen- in dependent tumours. Other hormones (prolactin, insulin) induce the activity of glucose 6-phosphate dehydrogenase III rather than that of glucose 6-phosphate dehydrogenase I in normal mammary tissue. The idea of existence of a fine regulation of the enzyme activity through selective activation or repression of individual isozymes is confirmed.