An electron microscopic study of pyruvate carboxylase.

Pyruvate carboxylases, purified to homogeneity from sheep and chicken liver, have been examined in the electron microscope and found to have a splayed tetrahedral structure which, in some views, appears similar to that described for this enzyme isolated from yeast. The square-planar tetrameric image previously ascribed to pyruvate carboxylases from vertebrate sources was shown to be that of a molecule which is not only larger than pyruvate carboxylase, but also devoid of biotin.