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Inhibition of facto...
Inhibition of factor I by diisopropylfluorophosphate. Evidence of conformational changes in factor I induced by C3b and additional studies on the specificity of factor I
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- Nilsson Ekdahl, Kristina (author)
- Uppsala universitet,Institutionen för onkologi, radiologi och klinisk immunologi,Department of Clinical Immunology and Transfusion Medicine, University Hospital, Uppsala
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- Nilsson, U R (author)
- Uppsala universitet,Institutionen för onkologi, radiologi och klinisk immunologi
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- Nilsson, Bo (author)
- Uppsala universitet,Institutionen för onkologi, radiologi och klinisk immunologi
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(creator_code:org_t)
- 1990
- 1990
- English.
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In: Journal of Immunology. - 0022-1767 .- 1550-6606. ; 144:11, s. 4269-4274
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Abstract
Subject headings
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- The factor I-mediated cleavage of C3b, using factor H as a cofactor was completely inhibited by diisopropylfluorophosphate (DFP) when factor I and C3b were incubated with DFP before the addition of factor H. Inhibition, although to a lesser degree, was observed when factor H was present during DFP-exposure. No inhibition in factor I activity was seen when factor I and H were incubated with DFP either alone or together. It was also demonstrated that the 38-kDa subunit of factor I bound radiolabeled DFP when factor I and C3b together were exposed to DFP. These observations suggest that factor I interacts with C3b in a manner that exposes its catalytic site to DFP, an interaction that is independent of factor H. The inhibitory effect by DFP on factor I led us to further investigate the factor I cleavage products of iC3b, inasmuch as previous reports were ambiguous as to whether digestion occurs in the presence of DFP. Digestion of C3b bound to activated thiol Sepharose (ATS-C3b) in the presence of factor H at low pH and ionic strength and in serum by complement activation produced C3d,g- like fragments with apparent molecular mass of 41 and 43 kDa. These fragments were shown to have three different N-terminal and two different C-terminal ends. The major fragments had N-terminal sequences starting with Glu933, as shown by sequence determination. Traces of fragments extending beyond this point were also found, shown by Western blot analysis using a panel of mAb previously shown to bind to epitopes exposed within a region of C3 spanning residues 929 to 943, as well as a shorter fragment starting with Glu938. When digestion of C3b is carried out in the presence of DFP, the factor I level necessary for digestion is elevated and may explain how the first two cleavages producing iC3b but not the following giving C3d,g, can occur. The finding of several factor I cleavage sites in the C3d,g region of C3 demonstrates that factor I has a broad specificity, mainly for arginyl bonds. It has also been shown to digest a lysyl bond exposed in ATS- bound C3b.
Subject headings
- MEDICIN OCH HÄLSOVETENSKAP -- Medicinska och farmaceutiska grundvetenskaper -- Immunologi inom det medicinska området (hsv//swe)
- MEDICAL AND HEALTH SCIENCES -- Basic Medicine -- Immunology in the medical area (hsv//eng)
Keyword
- Immunology
- Immunologi
- Immunologi
- Immunology
Publication and Content Type
- ref (subject category)
- art (subject category)
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