Effect of small-molecule additives on ORFV CBP crystals. Crystals were grown in 1.80 M ammonium citrate tribasic pH 7.0 in the presence of no additives (a, e) or varying concentrations of a small-peptide cocktail containing Gly-Phe, Gly-Tyr and Leu-Gly-Gly (b, c, d), glucose (f, g, h) or a fixed amount (100 mM) of l-arginine (i, j). The protein concentration in (a)–(d) and that in (i) was 10 mg ml−1. The protein concentration in (e)–(h) and (j) was 18 mg ml−1. The concentration of the small-peptide cocktail was 0.033%(w/v) in (b), 0.083%(w/v) in (c) and 0.116%(w/v) in (d). The concentration of glucose was 93.75 mM in (f), 156.25 mM in (g) and 312.5 mM in (h). The crystals in (a) have approximate dimensions of 0.2 × 0.1 × 0.1 mm. The crystals in (d), (h), (i) and (j) have dimensions of approximately 0.7 × 0.3 × 0.3 mm.