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Subunit interactions in the first component of complement, C1.

S Lakatos
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Abstract

Interactions between C1q and other subunits of C1 were analyzed by sucrose gradient ultracentrifugation. A zone of dilute, radioiodine labelled C1q was sedimented through uniform concentrations of either C1r2C1s2, C1r2, C1r2 or C1s(2). The dissociation constants were found to be 3 x 10(-9) M and 6 x 10(-9) M for C1r2C1s2 and C1r2 binding respectively. Hill coefficients of 1 indicated no cooperativity in these bindings. Positive cooperativity was found in binding of C1s to C1q. Dissociation constants of 2 x 10(-6) M and 5 x 10(-8) M were obtained form computer modelling of a two step binding mechanism. No interaction was detected between C1q and activated C1r2. The data indicate that most of the interactions between C1q and C1r2C1s2 originates from a strong binding to the C1r2 moiety of the zymogen complex. This interaction is lost upon activation of C1r2.

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Binding SitesCentrifugation, Density GradientComplement Activating EnzymesComplement C1Complement C1qComplement C1rComplement C1sJournal ArticleResearch Support, Non-U.S. Gov't

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S Lakatos. 1987-12-16. Subunit interactions in the first component of complement, C1.. https://doi.org/10.1016/0006-291x(87)90377-9

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