SEQUENCE-ANALYSIS OF BETA-A3, BETA-B3, AND BETA-A4 CRYSTALLINS COMPLETES THE IDENTIFICATION OF THE MAJOR PROTEINS IN YOUNG HUMAN LENS

A combination of Edman sequence analysis and mass spectrometry identif ied the major proteins of the young human lens as alpha A, alpha B, be ta A1, beta A3, beta A4, beta B1, beta B2, beta B3, gamma S, gamma C, and gamma D-crystallins and mapped their positions on two-dimensional electrophoretic gels. The primary structures of human beta A1, beta A3 , beta A4, and beta B3-crystallin subunits were predicted by determini ng cDNA sequences. Mass spectrometric analyses of each intact protein as well as the peptides from trypsin-digested proteins confirmed the p redicted amino acid sequences and detected a partially degraded form o f beta A3/A1 missing either 22 or 4 amino acid residues from its N-ter minal extension. These studies were a prerequisite for future studies to determine how human lens proteins are altered during aging and cata ract formation.