Pyruvate Dehydrogenase Multienzyme Complex of Escherichia coli . Determination of the M sub(r) of the Lipoate Acetyltransferase Component

Lipoate acetyltransferase (E2) forms the structural core of the pyruvate dehydrogenase multienzyme complex of Escherichia coli . It comprises 24 polypeptide chains to which are bound multiple copies of the other two component enzymes, pyruvate decarboxylase (E1) and lipoamide dehydrogenase (E3). There is a continuing controversy over the stoicheiometry of polypeptide chains in the native complex. Inherent in this discrepancy is a disagrecement over the M sub(r) of the E2 polypeptide. This paper reports a study of the M sub(r) determination for E2. Gel filtration in guanidine-HCl was chosen as it is a method for which anomalous behaviour of proteins has not yet been reported and it is one which has resolved a similar discrepancy in the mammalian pyruvate dehydrogenase complex.