Estimate of the Molecular Weight of the Sarcolemmal Sodium Channel Using H₂O‐D₂O Centrifugation

Abstract: The sodium channel saxitoxin binding component from rat sarcolemma was solubilized with NP‐40 and centrifuged on sucrose gradients constructed in either D₂O or H₂O. When compared with a series of standard proteins the sedimentation behavior of the solubilized channel complex changed from an apparent S_20.w of 9.1 in H₂O to 6.1 in D₂O. From these observations, a true partial specific volume of 0.83 ml/g was calculated for the complex. A Stokes radius of 8.6 nm was estimated from Sepharose 6‐B chromatography in NP‐40. The calculated protein molecular weight of the lipid‐protein‐detergent complex based on these data is 560,000. The complex contains about 56% protein, and the calculated molecular weight of this component is 314,000 if a v for the protein of 0.74 ml/g is assumed.