The mature size of rat 4-aminobutyrate aminotransferase is different in liver and brain.
The amino acid sequence predicted from a rat liver cDNA library indicated that the precursor of beta-AlaAT I (4-aminobutyrate aminotransferase, beta-alanine-oxoglutarate aminotransferase) consists of a mature enzyme of 466 amino acid residues and a 34-amino acid terminal segment, with amino acids attributed to the leader peptide. However, the mass of beta-AlaAT I from rat brain was larger than that from rat liver and kidney, as assessed by Western-blot analysis, mass spectroscopy and N-terminal sequencing. The mature form of beta-AlaAT I from the brain had an ISQAAAK- peptide on the N-terminus of the liver mature beta-AlaAT I. Brain beta-AlaAT I was cleaved to liver beta-AlaAT I when incubated with fresh mitochondrial extract from rat liver. These results imply that mature rat liver beta-AlaAT I is proteolytically cleaved in two steps. The first cleavage of the motif XRX( downward arrow)XS is performed by a mitochondrial processing peptidase, yielding an intermediate-sized protein which is the mature brain beta-AlaAT I. The second cleavage, which generates the mature liver beta-AlaAT I, is also carried out by a mitochondrial endopeptidase. The second peptidase is active in liver but lacking in brain.
Kontani
Y
Y
Faculty of Nutrition, Kobe-Gakuin University, Kobe, Japan.
Sakata
S F
SF
Matsuda
K
K
Ohyama
T
T
Sano
K
K
Tamaki
N
N
D000612:4-Aminobutyrate Transaminase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000201:enzymology*; D003001:Cloning, Molecular; D017931:DNA Primers; D006801:Humans; D008099:Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011499:Protein Processing, Post-Translational; D051381:Rats; D017386:Sequence Homology, Amino Acid; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D017931:DNA Primers; D005680:gamma-Aminobutyric Acid; D000612:4-Aminobutyrate Transaminase