Screening and kinetic analysis of delta-crystallins with endogenous argininosuccinate lyase activity in the lenses of vertebrates.

Screening of lens homogenates from the representative species of five major classes of vertebrates was undertaken to search for delta-crystallin with argininosuccinate lyase activity. Purification and biochemical characterization of delta-crystallins from the avian and reptilian species revealed differences in their electrophoretic and kinetic properties in spite of their similar tetrameric structure of about 200 kDa in the native forms. Chicken delta-crystallin, in contrast to those obtained from duck, goose and caiman, is almost devoid of the enzymatic activity. Two-dimensional gel electrophoresis of lens homogenates indicated that in the chicken lens delta-crystallin is composed of a subunit with an isoelectric point of 5.9 and a subunit mass of 50 kDa whereas that of goose lenses possesses heterogeneous subunits with isoelectric points spreading in a range of 5.9 to 6.8. Immunological comparison of inactive and active delta-crystallins from the chicken, duck and caiman lenses established the apparent structural similarity of all delta-crystallins to the authentic enzyme regarding some of common surface epitopes, yet they are not completely identical. Kinetic constants for two of the active delta-crystallins, i.e. those from the duck and goose of the Anatidae family, were also determined and their catalyzed reaction was shown to conform to a random Uni-Bi kinetic mechanism similar to that of the argininosuccinate lyase from the bovine liver.