Chemical analysis and electron microscopy studies of human C1q prepared by different methods

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Abstract
Five differently isolated and purified human C1q preparation were examined by electron microscopy and analyzed by polyacrylamide gel electrophoresis in 0.1 % sodium dodecyl sulfate and 0.5 M urea. The amino acid and carbohydrate composition of C1q purified by the DNA method are reported and compared with results obtained ion C1q isolated by other procedures. Electron microscopy showed that all C1q preparation had six peripheral subunits connected by fibrillar strands to a central subunit. The presence of small amounts of dimers was also observed. The physico-chemical properties of the molecule are independent of the purification method used. The five C1q preparation labeled with 125I in presence of lactoperoxidase formed two types of noncovalently linked subunits. In each case the smaller (central) subunit contained over thirty times as much radioactivity as the larger (peripheral) subunit supposed to interact with immune complexes. Reduction adn alkylatin confirmed for each preparation the presence of three polypeptide chains, the smaller of which contained essentially all radioactivity.