Protein-Crystal Density by Volume Measurement and Amino-Acid Analysis

The densities of protein crystals have been determined by crystal-volume measurement and amino-acid analysis. For this purpose, protein crystals were freely mounted under humidity control by means of air-stream-crystal-regulated humidity. With a video system (charge-coupled-device camera) the two-dimensional shadow projections of crystals are recorded and by the method of back projection the crystal shape is reconstructed and the volume determined. It is shown that the method is independent of the crystal morphology by the consistency of the results from a number of different crystals and materials.