␣-Actinin is tyrosine-phosphorylated in activated human platelets (Izaguirre, G., Aguirre, L., Ji, P., Aneskievich, B., and Haimovich, B. (1999) J. Biol. Chem. 274, 37012-37020). Analysis of platelet RNA by reverse transcription-polymerase chain reaction revealed that ␣-actinin expressed in platelets is identical to the cytoskeletal/non-muscle isoform. A construct of this isoform containing a His 6 tag at the amino terminus was generated. Robust tyrosine phosphorylation of the recombinant protein was detected in cells treated with the tyrosine phosphatase inhibitor vanadate. The tyrosine phosphorylation site was localized to the amino-terminal domain by proteolytic digestion. A recombinant ␣-actinin protein containing a Tyr 3 Phe mutation at position 12 (Y12F) was no longer phosphorylated when expressed in vanadate-treated cells, indicating that tyrosine 12 is the site of phosphorylation. The wild type recombinant protein was not phosphorylated in cells lacking the focal adhesion kinase (FAK). Re-expression of FAK in these cells restored ␣-actinin phosphorylation. Purified wild type ␣-actinin, but not the Y12F mutant, was phosphorylated in vitro by wild type as well as a Phe-397 mutant of FAK. In contrast, no phosphorylation was detected in the presence of a kinase-dead FAK. Tyrosine phosphorylation reduced the amount of ␣-actinin that cosedimented with actin filaments. These results establish that ␣-actinin is a direct substrate for FAK and suggest that ␣-actinin mediates FAK-dependent signals that could impact the physical properties of the cytoskeleton.

Sulfonated polymer membranes play an important role in PEMFC (proton exchange membrane fuel cell). Series of sulfonated polyamides were prepared by polycondensation of a CF3-containing diamine with various ratios of terephthalic acid and 5-Sodiosulfoisophthalic acid. Sulfonated polyamides were characterized by 1H-NMR, FTIR and intrinsic viscosity. The resulting polyamides exhibited outstanding thermal stability. Membranes were prepared by solution casting, then characterized by determining ion-exchange capacity (IEC), water uptake, swelling ratio, proton conductivity and mechanical properties. With the gradual growth of sulfonic acid groups from 70% to 100% (molar ratio), IEC increased to 1.0223meq/g, and proton conducticity reached up to 3.82×10-2S/cm, while water uptake and swelling ratio remained in proper values. And the tensile strength of membranes was beyond 46.63MPa, which showed very good perspectives in PEMFC applications.