ELSEVIER Journal of Crystal Growth 178 (1997) 393-401 J ........ CRYSTAL GROWTH Growth kinetics of protein single crystals in the gel acupuncture technique Juan Manuel Garcia-Ruiz*, Abel Moreno I Laboratorio de Estudios Cristalogrhficos, Instituto Andaluz de Ciencias de la Tierra. CSIC-Universidad de Granada, Av. Fuentenueva s/n, E-18002 Granada, Spain Received 26 December 1995; accepted 25 November 1996 Abstract The growth of single crystals of tetragonal HEW lysozyme and thaumatin I into glass capillaries was monitored by time lapse video-microscopy. The crystals were obtained by unidirectional transport of the precipitating agent through capillaries of internal diameter ranging from 0.2 to 1.2 mm, using the gel acupuncture technique. For crystals growing from true protein solutions, the measured average growth rates varies with capillary diameter from 1.7 to 3.7 ,~/s for thaumatin and from 2.8 to 22 ~,/s for lysozyme. The measured average growth rates for crystals growing into gelled protein solutions were 1.8 ,~/s for thaumatin and 2.5 ,~/s for lysozyme. The trend in the variation of the growth rate with time is similar and suggests that, for capillaries with internal radius lower than 0.8 mm, diffusion dominates the global mass transport control. However, the existence of convection rolls near the crystal-solution interface and close to zones with high density gradient cannot be discarded. PACS: 81.10. -- h; 81.10.Aj Keywords. Protein; Growth rate; Lysozyme; Thaumatin; Gel 1. Introduction The accretion of a periodic arrangement of protein molecules with high degree of perfection involves phenomena taking place at the crystal/ solution interface. These phenomena are controlled *Corresponding author. Fax: + 34 58 243 384; e-mail: jmgruiz@goliat.ugr.es. Present address: Instituto de Quimica, Universidad Nacional Aut6noma de M6xico, Circuito Exterior, CU Coy- oacan, C.P. 04150, Mexico. by the local values of the driven force for phase transition, and also by the flow of growth units from the bulk solution towards the growing crystal faces. It is currently thought that diffusional control of the growth process reduces the number of defects enhancing the internal order of the crys- tals. The existence of density-driven convection tends to break the symmetry of the diffusion field around a crystal growing under ideal conditions and introduces local anisotropy in space and time. It follows that convective flow has to be minimized and this justifies present efforts in the design of 0022-0248/97/$17.00 Copyright ~) 1997 Elsevier Science B.V. All rights reserved Pll S0022-0248(96)01 188-8