SOLUBILIZATION AND CHEMICAL CHARACTERIZATION OF AN INSOLUBLE MATRIX PROTEIN IN THE GASTROLITHS OF A CRAYFISH, PROCAMBARUS-CLARKII

The gastrolith of the crayfish Procambarus clarkii contains a small am ount of an organic matrix that is mainly chitin and proteins, together with a large amount of calcium carbonate. As the first step to unders tand the mechanism of calcification, we tried to characterize matrix p roteins in the gastrolith. An insoluble matrix protein, referred to as gastrolith matrix protein, was made soluble with 1% SDS containing 10 mM dithiothreitol, and was purified by reverse-phase high-performance liquid chromatography. The protein had a molecular weight of about 50 ,500 and a blocked amino terminus. By enzymatic digestion and microseq uencing, five partial amino acid sequences with a total of 225 amino a cid residues were identified and found to include a repetitive sequenc e not reported previously.