Increase in Glutaminase Activity during the Growth Cycle of Cultured Human Diploid Fibroblasts

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Abstract
The activity of glutaminase per milligram of protein increased threefold after cultured human diploid fibroblasts were subcultured in fresh medium. The maximum activity was reached after 2 days of growth and decreased once the cells reached confluency. The increase of glutaminase activity was independent of the glutamine concentration between 0.2 and 2.0 mmol/1. In contrast, the specific activity of glutamate dehydrogenase was independent both of the glutamine concentration and the growth phase of the cultured cells. These results indicate that glutaminase, the first enzyme involved in the utilization of glutamine as an energy source, is elevated in rapidly dividing human diploid fibroblasts.