Buoyant densities of dissolved and crystalline lactate dehydrogenase from pig heart and pig muscle [cross-linked protein crystals, dimethylsuberimidate, cesium chloride, cesium sulfate, density gradient, equilibrium ultracentrifugation]
1978
Pedersen, T.G. | Bayne, S. | Ifft, J.B. | Ottesen, M.
Buoyant densities of the H(,4) and M(,4) isoenzymes of lactate dehydrogenase from pig, in both dissolved and crystalline cross-linked states, have been determined at neutral pH in concentrated CsCl solutions by equilibrium centrifugations in an ultracentrifuge. In both states, buoyant densities of the M(,4)-LDH were lower than those of the H(,4)-LDH, presumably due to the binding of the counterions and hydration water by ten additional charged amino acid residues present on the M(,4)-LDH. The cross-linked crystals had lower buoyant densities than enzymes in dissolved state consistent with the lower density of the cross-linking reagent. The variations in buoyant densities observed in CsCl solutions are in agreement with a previously described model for the water-and ion-binding to proteins which assigns almost all of the bound water to the charged amino acid side chain residues. In Cs(,2)SO(,4) solutions the buoyant densities of the H(,4)-LDH in both physical states were less than in CsCl, probably because strongly hydrated sulphate ions bind to the charged amino acid residues
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