Purification and expression of a processing protease on beta-alanine-oxoglutarate aminotransferase from rat liver mitochondria.

GABA[arrow beta]AlaAT convertase is an endopeptidase that processes brain-type 4-aminobutyrate aminotransferase (GABA AT; EC 2.6.1.19) to liver-type beta-alanine-oxoglutarate aminotransferase (beta-AlaAT I) in rats. Its molecular mass was 180 kDa as determined by gel filtration. A subunit molecular mass of 97652 Da was measured using MALDI-TOF MS. The N-terminal sequence of the purified GABA[arrow beta]AlaAT convertase was SRVEVSKVLILGSGGLSIGQAGEFDYSGSQAV- and was identical to residues 418-449 of carbamoyl-phosphate synthetase I (CPS I; EC 1.2.1.27) purified from rat liver. The subunit molecular mass and the N-terminal amino acid sequence suggested that GABA[arrow beta]AlaAT convertase was the 418-1305 peptide of CPS I. An expression vector containing the coding region of the 418-1305 peptide of rat CPS I was transfected into NIH3T3 cells and the extract of the cells showed GABA[arrow beta]AlaAT convertase activity.