Effect of supersaturation ratio on the growth rate and number of protease thermolysin crystals

Abstract

The effect of initial supersaturation ratio on the growth rate and number of protease thermolysin crystals was investigated at the initial supersaturation ratio of 8.9 to 17.9 and pH 7.0. The average diameter and number of thermolysin crystals were measured by dynamic light scattering during crystallization. The crystallization of thermolysin proceeded through two successive steps: the formation of primary particles and the formation of large crystals from the primary particles. The size of the primary particles was not affected by the initial supersaturation ratio and was about 60 nm in diameter. The growth rate of thermolysin crystals had a maximum at the initial supersaturation ratio of 9.5. On the other hand, the number of thermolysin crystals decreased with an increase of the initial supersaturation ratio, and turned to increase through a minimum at the initial supersaturation ratio of 13.4. The dependencies of the size and number of thermolysin crystals on the initial supersaturation ratio were explained by the successive two step mechanism of crystallization.