Studies on metrizamide-protein interactions.

1. The apparent density of catalase after isopycnic centrifugation in metrizamide gradients is dependent on the metrizamide concentration into which the enzyme is dissolved at the beginning of the centrifugation. 2. This different behaviour of the enzyme in metrizamide gradients is due to the formation of a metrizamide-protein complex which is more dense than the uncomplexed catalase. 3. A bimodal distribution of the catalase, with additional heavy bands, was only observed in metrizamide gradients in light water, where rather high metrizamide concentrations are needed even for a banding of the uncomplexed enzyme. 4. The half-life of the metrizamide-protein complex is less than 5 min. This was shown by spectroscopical measurements and band sedimentation analysis in an analytical ultracentrifuge.