STRUCTURAL PROTEINS OF MAMMALIAN LENS - REVIEW WITH EMPHASIS ON CHANGES IN DEVELOPMENT, AGING AND CATARACT

A third or more of the wet weight and almost all the dry material of the mammalian lens is protein. This protein may be fractionated into many components and most sections of this review deal with the major components. Capsular proteins which differ markedly from those of the body of the lens are discussed. Grinding or stirring the decapsulated lenses in water or dilute aqueous buffers does not extract all the protein into solution and the terms water-soluble and water-insoluble are used to describe the 2 fractions. These 2 fractions are largely different forms of the same proteins; different relative amounts of the 2 fractions are obtained under different experimental conditions. Much of the insoluble protein isolated from normal rat, normal human and cataractous human lens is produced artifactually during extraction from proteins that may be isolated in a soluble form if 02 is excluded. Much of the earlier literature on insoluble proteins from lens must be re-interpreted and the amount of insoluble protein produced in studying the relationship of the water-soluble proteins to the lens in vivo, especially for human lens must be considered. The water-soluble proteins, .alpha.- .beta.- and .gamma.-1 crystallins are discussed. The water-insoluble proteins including membrane proteins and proteins insoluble in dissociating solvents are discussed and related to the bulk lens proteins.