The subcomponent C1q of the first component of guinea pig complement: Purification and characterization

Guinea pig C1q was purified, in a highly active hemolytic form, by a combination of precipitation with chelating agents, CM-cellulose and Sepharose 6B. Yields ranged from 30 to 35% protein, and the activity of final preparations was in the range of 2 × 10¹³– 3 × 10¹³ C1q effective molecules/mg. The molecular weight of C1q was approximately 430,000, as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). C1q was shown to be composed of two non-covalently linked subunits of approximate molecular weights 46,500 and 45,000 in a molar ratio 2 : 1. On reduction, the higher molecular weight subunit gave two chains having approximate molecular weights of 24,500 and 23,000 in equimolar ratio, and the lower weight subunit gave one chain with a molecular weight of approximately 22,300. C1q contained hydroxyproline, hydroxylysine and a high percentage of glycine. Thus, the overall molecular structure of guinea pig C1q appears similar to that of human C1q.The antiserum against the purified C1q showed only one precipitation band with guinea pig whole serum of purified C1q on immunodiffusion analyses and was found to be monospecific.