STUDIES ON TETRAGONAL LYSOZYME CRYSTAL-GROWTH RATES

A computer-controlled apparatus able to simultaneously follow the face growth rate of up to 40 crystals was developed. This apparatus was us ed to investigate the effects of solution pH on the (110) and (101) fa ce growth rates of tetragonal lysozyme. Growth rates were measured at pH 4.0, 4.4, 4.8 and 5.2, in 0.1 M sodium acetate buffer with 5 % NaCl , 295 K. Initial crystal sizes ranged from 10 to 40 mum. Plots of log supersaturation ratio (either C/C(sat) or C/C(sat) - 1) versus log(gro wth rate) are not linear, typically having a slope of approximately 8 at the lowest growth rates determined (10(-6) mum s-1), which falls of f to a slope of approximately 2 at the highest growth rates (10(-2) mu m s-1) measured. Ratios of C/C(sat) ranged from 4 to > 20. The data sh ow that lower solubility solutions require higher supersaturation rati os for equivalent growth rates. Data for the growth rate of the (101) face at pH 4.0 were widely scattered, especially at lower supersaturat ion ratios. Time-lapse video of crystals at low supersaturations shows that initially only the (110) faces grow, leaving 'notches' at the (1 10)-(110) corners. These corners then fill in and macro-steps appear o n the (101) faces which rapidly move inward in the form of an octagon, restoring the crystal to a 'normal' appearance. This phenomenon has b een observed for tetragonal crystals grown in either still or flowing solutions. Flowing solutions at lower supersaturations also gave cases where the corners did not fill in, with the (110) faces continuing to grow out until growth ceased.