Tyrosine Microcrystals Produced by Digestion of Proteins with Pancreatic Enzymes

If serum albumin from several animals, including humans, at concentrations greater than about 60 mg/mL is combined with an aqueous extract of porcine or human pancreas, then massive amounts of microcrystals develop. Both raw blood serum, as well as a range of concentrated, pure proteins, when combined with the extract produced identical crystals. Morphologies of crystals and their aggregates did, however, show some dependence on the starting protein material. Crystals could be dissolved by boiling in water and recrystallized. By X-ray diffraction we showed the crystals to be l-tyrosine crystals, presumably a degradation product of the starting proteins. Amino acid analysis, supported by mass spectrometry, of even well washed crystals, however, consistently showed them to be composed of 20% to 30% of other amino acids. An atomic force microscopy investigation of the crystals revealed that the crystal surfaces were persistently coated with spherical particles about 3 nm in diameter. The particles are apparently micellar arrangements of oligopeptides. Some implications of our results with regard the appearance of tyrosine crystals in human tissues under pathological conditions, in tumors, and in natural products such as foods are discussed.