Metal binding to porcine pancreatic elastase: calcium or not calcium

Orthorhombic crystals of porcine pancreatic elastase have been grown in the presence of sodium sulfate and in the presence of sodium citrate plus calcium chloride. The observed differences in the diffraction patterns lead to the conclusion that elastase in its canonical Na₂SO₄ crystal form does not contain calcium in its metal-binding site but sodium instead.

Xenon derivatization of halide-soaked protein crystals

Crystals derived by soaking in bromide solutions can subsequently be derived under a xenon atmosphere. Intensity data collected to lower energy than the bromine absorption edge can be used to determine the xenon position and the resultant phase information used to determine the bromine substructure from data collected to higher energy than the bromine absorption edge.