Evidence for the chemical interaction of urease in solution

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Abstract
Electrophoretic-mobility data on urease have been obtained over the range pH 3.5-9.0; by interpolation it is confirmed that the isoelectric point of the enzyme in 0.10 ionic strength acetate buffers is 5-0 [plus or minus] 0.05. The material gave a single, rather symmetrical peak at all pH values. Sedimentation-velocity experiments generally gave at least three peaks, the relative proportions varying somewhat with the particular sample: the S20 values were approximately 19, 28 and 36s. In the presence of sulphite, samples which previously gave three peaks gave only the one with S20-19. and the specific enzymic activity increased. The concentration-dependence of the S of this species has been determined. Diffusion experiments gave much lower values of the diffusion coefficient in the absence of sulphite than in its presence, and the deviations from Gaussian form of the diffusion curves also changed markedly. The data are interpreted as indicating that dimers and trimers tend to be formed in urease solutions, but that the system is not one rapid quilibrium: the polymers are probably formed by intermolecular disulphide crosd-linkages.