Quantitative analysis of myofibrillar protein subunits: demonstration of large molar excesses of myosin light chains in rabbit ventricular myocardium.

We describe a method for the complete solubilization and quantitative analysis of individual myofibrillar proteins in whole tissue homogenates of ventricular myocardium using gradient dodecyl sulfate polyacrylamide gel electrophoresis and staining with 125I-labeled Coomassie brilliant blue. The procedure allows for the simultaneous quantification of myosin heavy chain, myosin light chain, phosphorylatable myosin light chain and actin from as little as 50 mg of tissue. Within-assay and between-assay variations range from 8.0% to 12.6% for each protein subunit. The method was applied to the determination of the subunit stoichiometry of purified myosin, and to the measurement of myosin and actin concentrations in the neonatal and adult rabbit heart. Furthermore, we provide quantitative biochemical evidence for the existence of large molar excesses of myosin light chains in tissue homogenates of both neonatal and adult rabbit ventricular myocardium.