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The role of C4-binding protein and {beta }1H in proteolysis of C4b and C3b

The role of C4-binding protein and {beta }1H in proteolysis of C4b and C3b Two forms of C4-binding protein (C4-bp) (C4-bp low, C4-bp high), which differ slightly in net charge and apparent molecular weight, as determined by SDS- PAGE, were separated by ion-exchange chromatography and contaminants removed with specific antisera. Both forms of C4-bp served as cofactors for the cleavage of C4b in solution by C3b inactivator, and the resulting fragments of the a'-chain of C4b had identical molecular weights. In addition, similarly to β1H, C4-bp low or high served as cofactors for the cleavage of fluid phase C3b by C3bINA. However, important quantitative differences between the activities of C4-bp and β1H were observed. With regard to C3b in solution, the cofactor activity of β1H was {approximately equal to}20 times greater than that of C4-bp on a weight basis. In relation to cell-bound C3b, the differences in activity were even more marked. Whereas β1H enhanced the effects of C3bINA on the erythrocyte intermediate EC3b, inhibiting the assembly of EC3bBb, C4-bp was without effect even at concentrations {approximately equal to}300 times greater than β1H. Therefore, under physiological conditions, it is likely that β1H is the key protein which controls the function of C3b, and that C4-bp activity is directed mainly toward the cleavage of C4b. We also examined the relation between C4-bp and the C3b-C4bINA cofactor described by Stroud and collaborators (3, 4). By functional, physico-chemical and immunological criteria, they are the same protein. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Experimental Medicine Rockefeller University Press

The role of C4-binding protein and {beta }1H in proteolysis of C4b and C3b

Fujita, T; Nussenzweig, V
The Journal of Experimental Medicine , Volume 150 (2): 267 – Aug 1, 1979
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Publisher
Rockefeller University Press
Copyright
© 1979 Rockefeller University Press
ISSN
0022-1007
eISSN
1540-9538
DOI
10.1084/jem.150.2.267
Publisher site
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Abstract

Two forms of C4-binding protein (C4-bp) (C4-bp low, C4-bp high), which differ slightly in net charge and apparent molecular weight, as determined by SDS- PAGE, were separated by ion-exchange chromatography and contaminants removed with specific antisera. Both forms of C4-bp served as cofactors for the cleavage of C4b in solution by C3b inactivator, and the resulting fragments of the a'-chain of C4b had identical molecular weights. In addition, similarly to β1H, C4-bp low or high served as cofactors for the cleavage of fluid phase C3b by C3bINA. However, important quantitative differences between the activities of C4-bp and β1H were observed. With regard to C3b in solution, the cofactor activity of β1H was {approximately equal to}20 times greater than that of C4-bp on a weight basis. In relation to cell-bound C3b, the differences in activity were even more marked. Whereas β1H enhanced the effects of C3bINA on the erythrocyte intermediate EC3b, inhibiting the assembly of EC3bBb, C4-bp was without effect even at concentrations {approximately equal to}300 times greater than β1H. Therefore, under physiological conditions, it is likely that β1H is the key protein which controls the function of C3b, and that C4-bp activity is directed mainly toward the cleavage of C4b. We also examined the relation between C4-bp and the C3b-C4bINA cofactor described by Stroud and collaborators (3, 4). By functional, physico-chemical and immunological criteria, they are the same protein.

Journal

The Journal of Experimental Medicine – Rockefeller University Press

Published: Aug 1, 1979

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