Changes in the levels of translatable glutaminase mRNA during onset and recovery from metabolic acidosis

The amount of the mitochondrial glutaminase present within rat kidney is increased 5-fold during chronic metabolic acidosis. This adaptive response is due to a corresponding increase in the relative rate of glutaminase synthesis. Poly(A+) RNA was purified from the kidneys of control, 7-day acidotic, and 2-day recovered rats and then fractionated by electrophoresis on a low melting temperature agarose gel. Translation of the fractionated RNA in a rabbit reticulocyte lysate yields a 72,000-dalton protein that is specifically precipitated by anti-glutaminase IgG. The level of this protein is at least 3-fold greater in the translation products of the fractionated poly(A+) RNA derived from the acidotic vs. control or recovered rats. Therefore, the 72,000-dalton product of translation is the apparent precursor to the 68,000- and 65,000-dalton proteins that are contained in the mitochondrial glutaminase. From its relative electrophoretic mobility, the size of the glutaminase mRNA was estimated to be approximately 6.5 kilobases. The relative levels of translatable glutaminase mRNA were determined by using unfractionated poly(A+) RNA prepared from rats at various times following onset and recovery from acidosis. The observed increase occurred gradually, requiring 7 days to reach a maximal induction of 4.2-fold. The increase could be due to the increased transcription of a stable mRNA (t1/2 approximately 3 days). However, 2 days of recovery was sufficient to return the level of translatable glutaminase mRNA to normal. Thus, the selective inactivation or the altered stability of the glutaminase mRNA must also contribute to the regulation of the glutaminase gene expression.