Regulation of Hepatic Amino Acid Transport and Partial Purification of the System A Carrier
Amino acid transport across the plasma membrane is an important site for metabolic regulation. Indeed, in many instances transport actually represents the first step of catabolism. Evidence from several laboratories suggests that transport into the hepatocyte is the rate-limiting step for alanine metabolism when tested at physiological levels of the substrate (Christensen, 1983). The general importance of amino acid flows between the major tissues of the body has been reviewed by Christensen (1982). The concept of metabolic control via translocation of nutrients across the plasma membrane is not new; Exton et al. (1970) proposed that substrate supply was a key regulator of amino acid-dependent gluconeogenesis nearly two decades ago. More recently, Christensen (1983) has postulated that concurrent changes in hepatic amino acid metabolism and accumulation ensure that transport across the plasma membrane remains rate-limiting over a wide range of extracellular substrate concentrations. Data from our laboratory indicate that the hepatic utilization of several amino acids for de novo glucose synthesis may be limited by availability.
KeywordsUrea Proline Dexamethasone Alanine HEPES
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