Cellular location and partial characterization of the alanine aminotransferase in ribbed mussel gill tissue

Differential centrifugation of ribbed mussel gill tissue homogenates and extraction of the mitochondrial fraction demonstrated that most (72%) alanine aminotransferase (AlAT) activity was mitochondrial. Subsequent characterization of the cytosolic activity demonstrated properties identical to those demonstrated by the mitochondrial enzyme. Both enzyme fractions showed little variation in Vmax with pH, had low Km's for ketoacid substrates, and were inhibited by aminooxyacetate (AOA), L‐cycloserine, and β‐chloro‐L‐alanine. It appears that the AlAT in ribbed mussel gill tissue is strictly mitochondrial and that alanine production during hypoxia or hyperosmotic stress must be mitochondrial.