Physical Properties of Spinach Chloroplast Lamellar Proteins

Abstract

Treatment of purified spinach chloroplast lamellae with dodecylsulfate and butanol effectively stripped the protein free of lipid. The lipid-free protein fraction was studied by spectrophotometry and analytical untracentrifugation. The protein fraction was found to consist of a large quantity of heme-free protein and the 2 cytochromes f and b6. The absorption maxima of the a and /3 bands of the ferrocytochromes did not appear to be significantly modified by low concentrations of detergent. In the analytical ultra-centrifuge, the protein fraction appeared as a single broad boundary exhibiting an association-dissociation equilibrium. The mean sedimentation coefficient at infinite dilution was found to be 2.3 x 10-13s and the diffusion coefficient 9.1 x 10-7 cm2 sec-1. Hence, the average molecular weight of the proteins was about 22,000 g.mole-1. This value can only be considered approximate, owing to the uncertain extrapolation of the sedimentation velocity data and to the assumed partial specific volume of the proteins. Assuming the proteins to be spherical, the diameter of the proteins was about 40 A. It is suggested that these units comprise a fundamental repeating structural unit in the lamellae.