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gamma-Crystallin isolated from the shark of cartilaginous fishes was compared with the cognate gamma-crystallin from the carp of bony fishes. Distinct differences in amino acid compositions, primary, secondary and tertiary structures were found. The most salient features of shark gamma-crystallin lie in the fact that this crystallin possessed a significant alpha-helical structure in the peptide backbone as revealed by circular dichroism study, in contrast to those orthologous gamma-crystallins from other vertebrate species including bony fishes which all show a predominant beta-sheet secondary structure. The tertiary structure as reflected in the intrinsic microenvironments of various aromatic amino acids in the native crystallins also shows unambiguous differences between these two classes of gamma-crystallins. N-Terminal sequence analysis corroborates the structural differences between shark and carp gamma-crystallins. gamma-Crystallin from the more primitive shark seems to be more in line with the main evolutionary phylogeny leading to the modern mammalian gamma-crystallin.

Four major gamma-crystallin subfractions have been isolated from the carp (Cyprinus carpio) and their N-terminal sequences determined by Edman protein sequencing. Extensive homologies indicative of close relatedness in their primary structure were found in these four gamma-crystallin polypeptides. Comparison of the carp N-terminal sequences with those of mammalian and amphibian gamma-crystallins also showed a high degree of homology present in their N-terminal segments despite the dissimilarity of amino acid compositions of fish gamma-crystallins to those of higher classes of vertebrates. The distinct yet closely-related partial sequences of carp gamma-crystallins could account for the profound microheterogeneity detected in the characterization of carp crystallins, suggesting the presence of a multigene family for gamma-crystallin in the lowest class of vertebrates, i.e. the fish.

Lens crystallins were isolated from homogenates of reptilian eye lenses (Caiman crocodylus apaporiensis) by gel-permeation chromatography and characterized by gel electrophoresis, and amino acid and N-terminal sequence analyses. Four fractions corresponding to alpha-, delta/epsilon/beta-, beta- and gamma-crystallins were identified on the basis of their electrophoretic patterns as revealed by SDS gel electrophoresis. Comparison of the amino acid contents of reptilian crystallins with those of mammals suggests that each orthologous class of crystallins from the evolutionarily distant species still exhibits similarity in their amino acid compositions and probably sequence homology as well. All fractions except that of gamma-crystallin were found to be N-terminally blocked. N-terminal sequence analysis of the purified gamma-crystallin subfractions showed extensive homology between the reptilian gamma-crystallin polypeptides themselves and also those from other vertebrate species, suggesting the existence of a multigene family and their close relatedness to gamma-crystallins of other vertebrates.