Cataracts result from any opacification of the normally clear lens of the eye. Since cataracts are a leading cause of blindness, studies determining the cause of cataract are an active area of vision research. Our interest is in the changes occurring in the structural proteins of the lens when cataracts form. These structural proteins are called crystallins. Crystallins are some of the oldest proteins found in the body, since ones found in the center of the lens were synthesized before birth and remain with us for our entire lives. Due to their age, these proteins undergo extensive modifications, including proteolytic cleavage, deamidation, phosphorylation, and oxidation. The challenge in this research is to distinguish between normal age-related modifications and unique modifications causing cataract. To make this distinction, my group analyzes the structure of crystallins using mass spectrometry. Measurement of the molecular mass of the crystallins and their peptides allows an unambiguous identification of their modifications. Once the modifications unique to crystallins from cataractous lenses are known, it will be possible to model how the alterations cause these proteins to lose their normal transparency. Hopefully, this information will be used to help develop agents to slow the rate of cataract formation.Mass spectrometric analysis is also useful to identify and analyze proteins in other research projects. Our future interest is in the growing field of proteomics, which uses mass spectrometry to both identify proteins and quantify changes in their relative abundance during disease. This field becomes increasingly important as new genes are sequenced and complete databases of all proteins found in humans and other species becomes available. A growing interest of our group is to develop new methodologies to measure global changes in relative protein abundance in complex protein mixtures using stable isotope tagging of peptides. These analysis provide opportunities for research using both biochemical and informatics tools.