The Molecular Weight and other Properties of Aspartate Aminotransferase from Pig Heart Muscle

Abstract

Convenient methods for the purification of the soluble aspartate aminotransferase from pig heart muscle are described. The enzyme obtained is homogeneous in the ultracentrifuge and to starch gel electrophoresis at about pH 9.0. At lower pH, as first described by Fasella et. al. [1], a number of electrophoretically distinct species can be detected. Some of the properties of these are reported. The currently accepted value of the molecular weight of the enzyme is incorrect: ultracentrifuge studies gave a value of 78,600 ± 2,400 (23 determinations). Gel filtration experiments led to a similar value. Titration of apoenzyme with cofactor gives values of the equivalent weight of the protein which vary with the enzymic specific activity. Extrapolation to the maximum specific activity leads to a value for the equivalent weight of about 40,000. The enzyme has, therefore, two cofactor binding sites.