Fig. 4.

Rat-like mutations in the amino acid region 198–207 of the YFP–dog-β₁ impair (YFP–β₁)–β₁ interactions. (A) Western blot analysis using antibodies against YFP and Na⁺/K⁺-ATPase β₁ shows that immunoprecipitation of YFP–β₁ resulted in co-precipitation of the endogenous Na⁺/K⁺-ATPase β₁ subunits from cell lysates of MDCK cells expressing the wild-type YFP–dog-β₁, or its mutants or the wild-type YFP–rat-β₁. (B) Densitometric quantification of the results presented in A was performed by dividing a signal from the antibody to β₁ by the corresponding signal from the antibody to YFP. The comparative bar graph shows these ratios as a percentage of the ratio obtained for the wild-type YFP–β₁. The results of quantification indicate that amino acid substitutions and insertion in the amino acid region 198–207 decreased the amount of YFP–β₁-co-immunoprecipitated endogenous β₁ subunits. The positions of the amino acid residues mutated are shown in Fig. 3A. WT, wild-type; error bars, ±s.d. (n=3); *, significant difference from the ‘WT-YFP–dog-β1’, P<0.01, Student's t-test.