Identification of the calmodulin-binding components in XXXX lens plasma membranes.

@entity11750 @entity1025 @entity3208 @entity8723 @entity460 @entity141 @entity71413 @entity291
Lens membranes, purified from @entity291 lenses, have been labeled by covalent cross-linking to membrane-bound 125I-calmodulin with @entity11750 . Electrophoretic analysis in @entity3208 demonstrated two major 125I-containing products of Mr = 49 000 and 36 000. That the formation of these two components was specifically inhibited by unlabeled calmodulin, or calmodulin antagonists, would indicate that the formation of these components was calmodulin-specific. The size of these two 125I-labeled components was unchanged over a range of 125I-calmodulin or @entity11750 concentrations indicating that they represent 1:1 complexes between 125I-calmodulin (Mr = 17 000) and Mr-32 000 and Mr-19 000 lens membrane components respectively. Although formation of both cross-linked components exhibited an absolute dependence on @entity1025 , the autoradiographic intensity of these components was enhanced when @entity141 was included with Mg2+ during the cross-linking reaction. Labeling was maximal in 10 mM @entity8723 and approximately 1 microM @entity141 . Treatment of lens membranes with chymotrypsin resulted in the cleavage of @entity71413 (the major lens membrane protein), with the appearance of a major proteolytic fragment of Mr = 22 000. This proteolysis was not associated with any significant change in either the size or amount of the 125I-calmodulin-labeled membrane components. These results suggest that calmodulin interacts with two membrane proteins, but not significantly with @entity71413 , in the intact lens cell membrane. Our results indicate the need to maintain caution in interpreting direct @entity460 plus calmodulin effects on @entity71413 and lens cell junctions.
