NUCLEOTIDE-SEQUENCE OF A CDNA CODING FOR BOVINE MITOCHONDRIAL ASPARTATE-AMINOTRANSFERASE

Aspartate aminotransferase is a pyridoxal-phosphate dependent enzyme w hich plays a key role in cell metabolism. We describe the cloning and sequence analysis of the cDNA encoding bovine mitochondrial aspartate aminotransferase and compare the sequence with those of isoenzymes fro m other mammalian species. An adult bovine heart cDNA library construc ted in lambda 1 gt11 was screened using two P-32-end labeled synthetic oligonucleotides. From the screening of the cDNA library two positive clones were isolated. A subclone in pEMBL18, 6B2, generated from the longest recombinant phage was further analyzed. This clone contains an insert of 2500 bp with an Open Reading Frame of 1287 bp that encodes a protein of 430 amino acids. The deduced amino acid sequence confirms previous results obtained by mass spectrometric sequencing, We calcul ated the percentage of amino acid identity for each protein pair and f or each comparison the average number of amino acid substitution per s ite (K-aa); the lowest K-aa values were obtained from the comparison b etween the bovine and pig enzymes. This study shows that the rate of e volution of mammalian mitochondrial AspAT is lower and more constant t han the equivalent cytosolic enzyme and adds to the growing body of kn owledge on the evolution of the aspartate aminotransferase. The sequen ce data have been deposited on the EMBL Sequence Data Bank (accession No Z25466).