CONTROL OF NUCLEATION OF PROTEIN CRYSTALS

Control of nucleation may be needed to obtain a reliable supply of lar ge protein crystals, when standard techniques give many small or twinn ed crystals. Heterogeneous nucleation may be controlled by the use of fine filters, with the elimination of airborne contaminants by working under paraffin oil. The area of contact with the supporting vessel al so has an important effect. A heterogeneous nucleant for lysozyme (ide ntified earlier) has been shown to be effective for carboxypeptidase G (2) Control of homogeneous nucleation (previously demonstrated by dilu tions of a nucleating sample after various times of incubation) may al so be achieved by incubating a sample at 1 temperature, where nucleati on can occur, and changing the temperature to conditions where there i s growth but no nucleation.