Hydrodynamic Parameters of the Detergent‐Solubilised Hydrogenase from Paracoccus denitrificans

Abstract

The hydrogenase from Paracoccus denitrificans, which is an intrinsic membrane protein, has been solubilised from membranes by Triton X-100. The partial specific volume of the solubilised protein has been determined using sucrose density gradient centrifugation in H₂O and ²H₂O. The values of the specific volumes of hydrogenase, measured in the presence or absence of Triton X-100, are 0.73 and 0.74ml. g⁻¹, respectively, indicating that hydrogenase binds much less than one micelle of Triton X-100. The sedimentation coefficient of hydrogenase is increased from 10.4 S to 15.9 S on removal of detergent. The Stokes' radius of hydrogenase, determined by gel filtration on Sepharose 6B, is 5.5 nm in the presence of Triton X-100 compared to 6.7 nm in the absence of detergent. The apparent molecular weight therefore increases from 242500 to 466000 on removal of detergent. In the presence of urea and sodium dodecylsulphate, the hydrogenase has an apparent molecular weight of 63000. The enzyme therefore behaves as a non-covalently linked tetramer in the presence of Triton X-100. Removal of Triton X-100 results in association of tetramers to form octamers.