alpha m-Crystallin: the native form of the protein?

Evidence is presented that alpha-crystallin isolated at 37 degrees C exists as a species, alpha m, which has a minimum molecular weight of about 320000 and a sedimentation coefficient of about 12 S. The amino acid composition, subunit distribution, near- and far-UV CD spectra and immunochemical properties were identical to those of the previously studied, 19 S protein, alpha c-crystallin (minimum molecular weight, 635000). It was demonstrated that only alpha m-crystallin was present in 37 degrees C lens extracts and that cooling of lenses or extracts resulted in a conversion of alpha m- to alpha c-crystallin. This conversion appears to be a general phenomenon, independent of age or species. It was concluded that alpha c-crystallin is an aggregate, produced by cooling, and that alpha m-crystallin is more likely to represent the in vivo form of the protein.