Figure 6. Identification of 100 KD protein tyrosine-phosphorylation in response to myometrial stretch.

A. Stretch-induced tyrosine phosphorylation in human myometrium. Term pregnant uterine smooth muscle strips unstretched or stretched to 2x slack length for 7 min. Coomassie blue staining of anti-phosphotyrosine immunoprecipitates separated by 10% SDS-polyacrylamide gel electrophoresis (n = 2). B. Mass spectrometric identification of the 100 kD band. The protein band was excised from the gel. There is a 281/911 (31%) sequence coverage with 23 peptides matched to alpha 4 actinin, (in yellow) and 19% sequence coverage with 13 peptides matched to alpha 1 actinin (not shown). C. Alpha actinin is tyrosine phosphorylated by stretch in human myometrium. Homogenates of stretched and unstretched term pregnant human uterine smooth muscle were immunoprecipitated (IP) with an anti-phospho-tyrosine antibody and western immunoblotted (IB) with an alpha-actinin antibody. The graph shows the average densitometry from 5 independent experiments. The inserts are typical western blots of immunoprecipitates. *p<0.05 compared to unstretched control samples.