The Soluble Proteins of the Lens.

A review of recent work upon lens proteins suggests that Morners concept of three soluble lens proteins may still be tenable. This conclusion is based upon consideration of physical and chemical studies. Ultracentrifugal investigations of alpha crystallin indicate that it is composed of a number of different-sized aggregates of subunits held together by noncovalent forces. Studies at various pH's and toiih a number of solvents indicate that the size of the aggregates is dependent upon their environment. An average unit size of approximately 4 x 10* was observed in 7M urea. The dissociation may be reversed by returning the protein preparation to neutral aqueous conditions. Amino acid analyses of fractionated alpha crystallin aggregates indicates that they have the same or very similar composition. Amino acid analyses of the isolated subunits of alpha crystallin lead to a similar conclusion. Studies upon beta crystallin also indicate that it is composed of aggregates of smaller units. The amino acid compositions of isolated beta aggregates also appear to be very similar. The amino acid composition, N terminal sequence, and immunochemical reactivity of the gamma crystallins reported by Bjo'rk support the concept that the gamma crystallins are very closely related. Thus each of the crystallins appears to be composed of a group of species very similar in composition.