Purification, Properties, and Identity of Liver Mitochondrial Tyrosine Aminotransferase
Year: 1971
Type: article
Abstract: Mitochondrial tyrosine aminotransferase (l-tyrosine + 2-oxoglutarate = p-hydroxyphenylpyruvate + l-glutamate, EC 2.6.1.5) has been purified about 900-fold to homogeneity from rat liver and was crystallized. The enzyme is cationic and has a molecular weight of approximately 90,000, determined by amino acid composition and molecular sieve chromatography and of 114,000 by sedimentation analysis. It catalyzes the conversion of tyrosine to p-hydroxyphenylpyruvate and the reverse reaction. From the reverse direction with p-hydroxyphenylpyruvate, the reaction has a 3-fold greater rate with l-glutamate as cosubstrate than with aspartate. In the forward direction with l-tyrosine and α-ketoglutarate or oxaloacetate as cosubstrate, l-aspartate, α-methyl-l-aspartate, and β-methyl-l-aspartate are potent inhibitors. With α-ketoglutarate, amino acids were effective as cosubstrates in the following order of activity: l-aspartate g l-phenylalanine g l-cysteine g l-tyrosine g monoiodo-l-tyrosine = dihydroxy-l-phenylalanine g l-tryptophan g l-methionine = l-asparagine = p-chloro-l-phenylalanine. Evidence based on substrate specificity, inhibition by common substrates, inhibition by specific antibodies upon enzyme activity, and physical chemical properties indicate that the mitochondrial tyrosine aminotransferase is identical with mitochondrial aspartate aminotransferase (laspartate: 2-oxoglutarate aminotransferase, EC 2.6.1.1). This activity relationship would then distinguish this enzyme from the tyrosine aminotransferase and aspartate aminotransferase found in cytosol on the basis of properties and function.
Source: Journal of Biological Chemistry
Authors: James E. Miller, Gerald Litwack
Institution: Temple University
Language: English
Subfield: Biochemistry
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $3,430
OpenAlex ID: W1517976100