Study of the Zn‐containing dd‐carboxypeptidase of Streptomyces albus G by small‐angle X‐ray scattering in solution

Abstract

Study of the Zn2+‐containing d‐alanyl‐d‐alanine‐cleaving carboxypeptidase of Streptomyces albus G by small‐angle X‐ray scattering in solution yielded the following molecular parameters: radius of gyration R= 1.82 ± 0.05 nm; largest diameter D= 5.9 ± 0.2 nm; relative molecular mass Mr= 17000 ± 2000; volume V ∼ 35 ± 2 nm3; degree of hydration: 0.25 ± 0.02 g water/g protein. By reference to theoretical scattering curves of rigid triaxial homogeneous bodies, a model which fits all experimental data is an elliptical cylinder. Such a model is compatible with that observed in the crystal structure. At those high concentrations necessary to form inactive enzyme‐ligand associations the non‐competitive β‐lactam inhibitors, cephalothin and cephalosporin C, drastically altered the scattering behaviour of the protein. Copyright © 1984, Wiley Blackwell. All rights reserved