Phosphorylation of the band 4.1-like proteins of the bovine lens.

Crude membrane fractions prepared from the superficial cortical fiber cells of bovine lenses were incubated with [gamma-32P]-ATP. Membrane-associated 4.1-like proteins were then immunoprecipitated and analyzed for 32P-incorporation. Band 4.1-like proteins of 150 kd, 80 kd, and 78 kd were found to be labeled in a time-dependent fashion, with the 150 kd protein incorporating label at an 8-fold greater rate than the 80 kd and 78 kd proteins. Addition of cAMP or Ca2+ to the membrane preparations stimulated the phosphorylation of all three of these proteins. Our results indicate that the 4.1-like proteins of the lens fiber cell share with band 4.1 of the RBC the characteristic of being substrates for cAMP-independent and cAMP-dependent protein kinases.