Two-dimensional database of mouse liver proteins. An update

We updated the two-dimensional protein database for mouse liver. Microsomal and cytosolic fractions of the liver proteins from male mice were separate d by two-dimensional electrophoresis. The proteins were identified by Matri x-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) on the basis of peptide mass fingerprinting, following in-gel digestion with tryps in and matching with the theoretical peptide masses of all known proteins f rom all species. Approximately 5800 spots, excised from 14 two-dimensional gels, were analyzed which resulted in the identification of about 2500 prot eins that were the products of 328 different genes. The database includes 1 12 newly identified gene products. The fractionation prior to two-dimension al electrophoresis was essential for the detection of the new proteins, 55% of which were found in the microsomal and 35% in the cytosolic fraction. T he more frequently identified proteins in the various gels were heat shock proteins, house-keeping enzymes, such as ATP synthase chains, disulfide iso merase, and structural proteins, such as tropomyosin. About 45% of the iden tified proteins were detected 1-3 times, 45% 4-9 times, and the rest 10 or more times. Most proteins were represented by many spots. In average, about 18-20 spots were detected per gene product.