2Present address: Department of Orthopedic and Surgery, University of Virginia, Charlottesville, Virginia 22903, USA
3Present address: Department of Surgery, Thomas E. Starzl Transplantation Institute, University of Pittsburgh, E1502 BST, 200 Lothrop Street, Pittsburgh, PA 15232, USA
* To whom correspondence should be addressed.
This article has been retracted.
Received March 8, 2005; Revision received March 24, 2005
Alanine is the most effective precursor for gluconeogenesis among amino acids, and the initial reaction is catalyzed by alanine aminotransferase (AlaAT). Although the enzyme activity increases during fasting, this effect has not been studied extensively. The present study describes the purification and characterization of an isoform of AlaAT from rat liver under fasting. The molecular mass of the enzyme is 17.7 kD with an isoelectric point of 4.2; glutamine is the N-terminal residue. The enzyme showed narrow substrate specificity for L-alanine with Km values for alanine of 0.51 mM and for 2-oxoglutarate of 0.12 mM. The enzyme is a glycoprotein. Spectroscopic and inhibition studies showed that pyridoxal phosphate (PLP) and free -SH groups are involved in the enzymatic catalysis. PLP activated the enzyme with a Km of 0.057 mM.
KEY WORDS: alanine aminotransferase, fasting, purification