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Transcriptional Control of Rat Hepatic Glutaminase Expression by Dietary Protein Level and Starvation^1,2,

Department of Nutritional Sciences, Cook College, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903

Mammalian liver possesses a unique isozyme of phosphate-activated glutaminase that is subject to long-term regulation. In rats during starvation or after consumption of diets containing high amounts of protein (60%), hepatic glutaminase activity was 100% higher than in rats fed a 20% protein diet. Conversely, rats fed low protein diets (0 and 5%) had lower hepatic glutaminase activity when compared with rats fed the 20% protein diet. Differences in activity with different dietary protein levels were not due to differences in the amount of food consumed. The relative abundance of mRNA encoding hepatic glutaminase was lower in rats fed 0% protein and higher in those starved or fed 60% protein diet when compared with rats fed the 20% protein diet. The mRNA elongation assay in hepatic nuclei isolated from these animals demonstrated that the rate of transcription of the glutaminase gene was also different in rats starved or fed different levels of dietary protein. Overall, the results indicate that differences in hepatic glutaminase activity in rats starved or fed different levels of protein are mainly due to differences in the rate of transcription of the gene. In this way the regulation of hepatic glutaminase expression is similar to that seen for other enzymes involved in hepatic amino acid catabolism but differs markedly from that of renal glutaminase, in which changes in transcription rate are not observed and alterations of mRNA turnover are the principle mechanism of long-term regulation.

KEY WORDS: • glutaminase • liver • rats • dietary protein • gene expression • transcription

¹ Supported by grant DK37301 from the National Institutes of Health and Hatch Project 14161 of the New Jersey Agricultural Experiment Station.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed.

⁴ Current address: Department of Biochemistry, University of Novi Sad, Novi Sad, Yugoslavia.

Manuscript received 18 August 1993. Revision accepted 24 November 1993.