The X-ray structures of the crystals of bovine pancreatic β- trypsin soaked with amylamine as a probe were studied and compared in cydohexane and aqueous solution, respectively. It was shown that amylamine was occupied in the enzyme active site in cydohexane but not in aqueous solution. The crystal structure of the complex in cydohexane was determined at 0.2 nm resolution to a R-factor of 16.9% and a R_(free)-factor of 21.0% . The model includes one β-trypsin, two amylamine molecules, four sulfates, one calcium, and 135 water molecules. This X-ray structure analysis offers an approach to investigating an appropriate chemical compound to be an enzyme inhibitor or drug, and mapping the binding surface of crystalline protein with a probe which can bind to enzyme in organic medium but not in aqueous solution.

Key words: TRYPSIN, AMYLAMINE, PROTEIN, CRYSTAL STRUCTURE$