Studies on the Conformation of Yeast Pyruvate Decarboxylase in Solution by Small‐Angle X‐Ray Measurements

Abstract

Pyruvate decarboxylase, holo‐ and apo‐enzyme, was studied by X‐ray small‐angle scattering. A concentration series of the holo‐enzyme in 50 mM sodium phosphate buffer pH 6.8 was measured. The solutions were homodisperse and the following data could be determined: radius of gyration = 4.13 nm, molecular weight = 185000 (partial specific volume 0.751), volume = 400 nm3, hydration = 0.55 g H2O/g protein. The overall shape of the holo‐enzyme can be described by an elongated body (ellipsoid of revolution or double sphere) with an axial ratio of about 1:1:2.2. From the apo‐enzyme no homodisperse solutions could be obtained. There was always a mixture of particles, which had nearly the same radius of gyration as the holo‐enzyme, and larger aggregates. Therefore no detailed evaluation was possible. The partial specific volume was found to be identical with that of the holo‐enzyme within the limits of error. Copyright © 1973, Wiley Blackwell. All rights reserved