Crystal-growth kinetics of protein single crystals along capillary tubes in the gel-acupuncture technique

In attempts to obtain protein crystals of a sufficient size for structural studies, lack of knowledge of the physicochemical properties of protein solutions and of their crystal-growth behaviour lead to a bottleneck for drug design as well as for X-ray crystallography. Most formal investigations on crystal-growth phenomena have been focused on equilibrium studies, where the protein is soluble, and on the kinetics of crystal growth, which is related to both nucleation and crystal-growth phenomena. The aim of this work is to measure the crystal-growth rate along a capillary tube used as a growing cell. These experiments were carried out using the gel-acupuncture technique [García-Ruiz et al. (1993). Mater. Res. Bull. 28, 541-546; García-Ruiz & Moreno (1994). Acta Cryst. D50, 484-490; García-Ruiz & Moreno (1997). J. Cryst. Growth, 178, 393-401]. Crystal-growth investigations took place using lysozyme and thaumatin I as standard proteins. The maximum average growth rate obtained in the lower part of the capillary tube was about 35 A s-1 and the minimum average growing rate in the upper part of the capillary tube was about 8 A s-1. The crystal-growth rate as a function of the supersaturation was experimentally estimated at a constant height along the capillary tube.