THE CRITERIA OF PURITY USED IN THE STUDY OF LARGE MOLECULES OF BIOLOGICAL ORIGIN

Structure and function of factor X: properties, activation, and activity in prothrombinase. A retrospective in a historical context

The evolution of our understanding of the formation of thrombin from the postulated thrombokinase of Morawitz to activated Factor X and prothrombinase occurred during a period of nearly 100 years. During this time structure-function relationships have emerged and the roles of phospholipid surfaces, the accessory factor, Factor V and its activated form have been clarified. This paper summarizes this story with particular acknowledgement of the seminal contributions of Haskell Milstone.

Thrombin: An Approach to Developing a Higher-Order Reference Material and Reference Measurement Procedure for Substance Identity, Amount, and Biological Activities

Thrombin, the proteolytic enzyme that catalyzes the transformation of soluble fibrinogen to the polymerized fibrin clot, participates in multiple reactions in blood coagulation in addition to the clotting reaction. Although reference materials have existed for many years, structural characterization and measurement of biological activity have never been sufficient to permit claims of clear metrological traceability for the thrombin preparations. Our current state-of-the-art methods for protein characterization and determination of the catalytic properties of thrombin now make it practical to develop and characterize a metrologically acceptable reference material and reference measurement procedure for thrombin. Specifically, α-thrombin, the biologically produced protease formed during prothrombin activation, is readily available and has been extensively characterized. Dependences of thrombin proteolytic and peptide hydrolytic activities on a variety of substrates, pH, specific ions, and temperature are established, although variability remains for the kinetic parameters that describe thrombin enzymatic action. The roles of specific areas on the surface of the thrombin molecule (exosites) in substrate recognition and catalytic efficiency are described and characterized. It is opportune to develop reference materials of high metrological order and technical feasibility. In this article, we review the properties of α-thrombin important for its preparation and suggest an approach suitable for producing a reference material and a reference measurement procedure that is sensitive to thrombin’s catalytic competency on a variety of substrates.

An approximate ‘steady state’ condition in the ultracentrifuge

An analysis is developed for two-component systems in a modified steady-state condition which may be attained in the ultracentrifuge. The method depends on the sharpening effect which generally occurs across a moving boundary, because sedimentation coefficients increase with dilution; this effect is counteracted by diffusion and, accordingly, the sharpening and spreading effects may be made to balance by proper selection of the experimental conditions. Owing to radial dilution and the inhomogeneous field, a true steady state cannot occur, but certain characteristics of the boundary do become independent of time. With multi-component systems which yield a single boundary, the diffusional spreading is augmented by the effect of heterogeneity: thus a steady state, if attainable, can occur only when the gravitational field is increased to balance this effect also. When such systems are analysed in terms of the equations valid for two-component systems, the deviations from homogeneity are manifested as a difference between the apparent diffusion coefficient (i.e. the spreading coefficient) and the true diffusion coefficient. The analysis has been tested by application to a purified protein and a polydisperse mucopolysaccharide. It is shown that an approximately steady state is readily attainable under certain experimental conditions, and that the method provides a sensitive means of detecting impurities and characterizing heterogeneity, although the 2-component analysis is not adequate to interpret fully the behaviour of very polydisperse systems.

THE GLYCOSAMINOGLYCAN OF THE 'GROUND SUBSTANCE' OF RAT SKIN

The glycosaminoglycan was isolated from an isotonic saline extract of dry, fat-free rat skin in better than 80% yield. The product was virtually homogeneous as judged by electrophoresis on paper at several pH values, by electrophoresis on sponge rubber, and by fractional precipitation of the calcium and sodium salts with ethanol. The material corresponded to hyaluronate in electrophoretic mobility, solubility of its salts in ethanol, and in its content of a single hexosamine, glucosamine.

THE GLYCOSAMINOGLYCAN OF THE 'GROUND SUBSTANCE' OF RAT SKIN

The glycosaminoglycan was isolated from an isotonic saline extract of dry, fat-free rat skin in better than 80% yield. The product was virtually homogeneous as judged by electrophoresis on paper at several pH values, by electrophoresis on sponge rubber, and by fractional precipitation of the calcium and sodium salts with ethanol. The material corresponded to hyaluronate in electrophoretic mobility, solubility of its salts in ethanol, and in its content of a single hexosamine, glucosamine.