Characterization of a hexagonal crystal form of an enzyme of steroid metabolism, Δ5-ketosteroid isomerase: A new method of crystal density measurement

Abstract

A hexagonal crystal form ( P6 322, a = b = 65.38 A ̊ , c = 504 A ̊ ) of Δ 5-3-ketosteroid isomerase from Pseudomonas testosteroni (EC 5.3.3.1), grown at pH 5.5, has been characterized. The asymmetric unit contains four protomers ( M r = 13,394 each). This crystal form of the enzyme is more suitable for a high-resolution X-ray crystallographic structure determination than the monoclinic form (Westbrook et al., 1976). The protein content of the asymmetric unit was determined for both crystal forms by a novel and convenient technique which may have general applicability.