Spontaneous activation of the first component of human complement (C1) by an intramolecular autocatalytic mechanism

For biochemical characterization, the first component of human complement (C1) was reconstituted from physiologic concentrations of purified C1q, 125I C1r, and 131I C1s. Upon incubation at 37 degrees C, C1 spontaneously activated, as evidenced by the characteristic proteolysis of the C1r and C1s pol...

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Veröffentlicht in:The Journal of immunology (1950) 1982-06, Vol.128 (6), p.2500-2504
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description For biochemical characterization, the first component of human complement (C1) was reconstituted from physiologic concentrations of purified C1q, 125I C1r, and 131I C1s. Upon incubation at 37 degrees C, C1 spontaneously activated, as evidenced by the characteristic proteolysis of the C1r and C1s polypeptide chains as detected by SDS-PAGE analysis. This spontaneous C1 activation followed first-order kinetics (t 1/2 = 4 min and k = 0.173 min-1) with an activation energy of 19.1 kcal/mol. Spontaneous C1 activation was unaffected by the general protease inhibitor phenylmethylsulfonylfluoride (PMSF) but reversibly blocked by a known inhibitor of C1 activation, nitrophenylguanidinobenzoate (NPGB). Spontaneous C1 activation was measured at C1 concentrations ranging from 9 to 160 nM (i.e., 0.05 to 1.0 times physiologic concentrations). The data indicate that C1 spontaneously activates by an intramolecular autocatalytic mechanism, for first-order kinetics were observed over the entire concentration range with t 1/2 = 4 min at each concentration. However, the percentage of activable C1 decreased with dilution due to C1 dissociation (i.e., C1qr2s2 leads to C1q + C1r2s2). The observed concentration of C1 that spontaneously activated at each dilution equalled the concentration of C1 present as macromolecular C1. When reconstituted C1 was mixed with normal human serum (NHS) and then incubated at 37 degrees C, spontaneous C1 activation was completely inhibited. Pretreating NHS at 56 degrees C for 30 min destroyed its inhibitory activity. In conclusion, C1 spontaneously autoactivates at 37 degrees C by an intramolecular mechanism. This activation is suppressed in NHS.
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Upon incubation at 37 degrees C, C1 spontaneously activated, as evidenced by the characteristic proteolysis of the C1r and C1s polypeptide chains as detected by SDS-PAGE analysis. This spontaneous C1 activation followed first-order kinetics (t 1/2 = 4 min and k = 0.173 min-1) with an activation energy of 19.1 kcal/mol. Spontaneous C1 activation was unaffected by the general protease inhibitor phenylmethylsulfonylfluoride (PMSF) but reversibly blocked by a known inhibitor of C1 activation, nitrophenylguanidinobenzoate (NPGB). Spontaneous C1 activation was measured at C1 concentrations ranging from 9 to 160 nM (i.e., 0.05 to 1.0 times physiologic concentrations). The data indicate that C1 spontaneously activates by an intramolecular autocatalytic mechanism, for first-order kinetics were observed over the entire concentration range with t 1/2 = 4 min at each concentration. However, the percentage of activable C1 decreased with dilution due to C1 dissociation (i.e., C1qr2s2 leads to C1q + C1r2s2). The observed concentration of C1 that spontaneously activated at each dilution equalled the concentration of C1 present as macromolecular C1. When reconstituted C1 was mixed with normal human serum (NHS) and then incubated at 37 degrees C, spontaneous C1 activation was completely inhibited. Pretreating NHS at 56 degrees C for 30 min destroyed its inhibitory activity. In conclusion, C1 spontaneously autoactivates at 37 degrees C by an intramolecular mechanism. This activation is suppressed in NHS.</description><subject>Analysis of the immune response. Humoral and cellular immunity</subject><subject>Benzoates - pharmacology</subject><subject>Biological and medical sciences</subject><subject>Catalysis</subject><subject>Cell interactions</subject><subject>Complement Activating Enzymes</subject><subject>Complement Activation</subject><subject>Complement C1 - metabolism</subject><subject>Complement C1q</subject><subject>Complement C1r</subject><subject>Complement C1s</subject><subject>Fundamental and applied biological sciences. Psychology</subject><subject>Fundamental immunology</subject><subject>Guanidines - pharmacology</subject><subject>Humans</subject><subject>Immunobiology</subject><subject>Kinetics</subject><subject>Macromolecular Substances</subject><subject>Phenylmethylsulfonyl Fluoride - pharmacology</subject><subject>Protease Inhibitors - pharmacology</subject><subject>Temperature</subject><subject>Time Factors</subject><issn>0022-1767</issn><issn>1550-6606</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>1982</creationdate><recordtype>article</recordtype><sourceid>EIF</sourceid><recordid>eNqFkU9v1DAQxS1EVZbCJ0BIOSCghyzjOHHiY7XiT6VKHICzNXEc4sqOF9thtd8eh10qbj1ZevObZ817hLyisK2hFh_ujXPL7O2WVt2Wb6sG4AnZ0KaBknPgT8kGoKpK2vL2GXke4z0AcKjqS3LJq44yVm1I_Lb3c8JZ-yUWqJL5jcn4ufBjkSZdjCbEVCjvMqXntMrT4nD-K1ntVu39jl4X_bHIqplTQOetVovFUOCSvMKE9piMKpxWE84muhfkYkQb9cvze0V-fPr4ffelvPv6-XZ3c1eqmrWpbDQdgLbIeoFiaFuoFWUUBcDQMtqPnRoBWa26ocFuFA0K7JnmWgPUnagUuyJvT7774H8tOibpTFTa2tO5ss0p5jzYo2COlEIraAbZCVTBxxj0KPfBOAxHSUGunch_ncjcieRy7SRvvT7bL73Tw8POuYQ8f3OeY1Rox4CzMvEBE0ww3q3YuxM2mZ_TwQQto0NrsymVh8Phvw__ABXipgM</recordid><startdate>198206</startdate><enddate>198206</enddate><creator>Ziccardi, RJ</creator><general>Am Assoc Immnol</general><general>American Association of Immunologists</general><scope>IQODW</scope><scope>CGR</scope><scope>CUY</scope><scope>CVF</scope><scope>ECM</scope><scope>EIF</scope><scope>NPM</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>7T5</scope><scope>H94</scope><scope>7X8</scope></search><sort><creationdate>198206</creationdate><title>Spontaneous activation of the first component of human complement (C1) by an intramolecular autocatalytic mechanism</title><author>Ziccardi, RJ</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c437t-5e1d017a3b9a9d7704c131a900d731bf8cf0a34c8d5a8f95a9ab3e6ee004892c3</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>1982</creationdate><topic>Analysis of the immune response. Humoral and cellular immunity</topic><topic>Benzoates - pharmacology</topic><topic>Biological and medical sciences</topic><topic>Catalysis</topic><topic>Cell interactions</topic><topic>Complement Activating Enzymes</topic><topic>Complement Activation</topic><topic>Complement C1 - metabolism</topic><topic>Complement C1q</topic><topic>Complement C1r</topic><topic>Complement C1s</topic><topic>Fundamental and applied biological sciences. Psychology</topic><topic>Fundamental immunology</topic><topic>Guanidines - pharmacology</topic><topic>Humans</topic><topic>Immunobiology</topic><topic>Kinetics</topic><topic>Macromolecular Substances</topic><topic>Phenylmethylsulfonyl Fluoride - pharmacology</topic><topic>Protease Inhibitors - pharmacology</topic><topic>Temperature</topic><topic>Time Factors</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Ziccardi, RJ</creatorcontrib><collection>Pascal-Francis</collection><collection>Medline</collection><collection>MEDLINE</collection><collection>MEDLINE (Ovid)</collection><collection>MEDLINE</collection><collection>MEDLINE</collection><collection>PubMed</collection><collection>CrossRef</collection><collection>Immunology Abstracts</collection><collection>AIDS and Cancer Research Abstracts</collection><collection>MEDLINE - Academic</collection><jtitle>The Journal of immunology (1950)</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Ziccardi, RJ</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Spontaneous activation of the first component of human complement (C1) by an intramolecular autocatalytic mechanism</atitle><jtitle>The Journal of immunology (1950)</jtitle><addtitle>J Immunol</addtitle><date>1982-06</date><risdate>1982</risdate><volume>128</volume><issue>6</issue><spage>2500</spage><epage>2504</epage><pages>2500-2504</pages><issn>0022-1767</issn><eissn>1550-6606</eissn><coden>JOIMA3</coden><abstract>For biochemical characterization, the first component of human complement (C1) was reconstituted from physiologic concentrations of purified C1q, 125I C1r, and 131I C1s. Upon incubation at 37 degrees C, C1 spontaneously activated, as evidenced by the characteristic proteolysis of the C1r and C1s polypeptide chains as detected by SDS-PAGE analysis. This spontaneous C1 activation followed first-order kinetics (t 1/2 = 4 min and k = 0.173 min-1) with an activation energy of 19.1 kcal/mol. Spontaneous C1 activation was unaffected by the general protease inhibitor phenylmethylsulfonylfluoride (PMSF) but reversibly blocked by a known inhibitor of C1 activation, nitrophenylguanidinobenzoate (NPGB). Spontaneous C1 activation was measured at C1 concentrations ranging from 9 to 160 nM (i.e., 0.05 to 1.0 times physiologic concentrations). The data indicate that C1 spontaneously activates by an intramolecular autocatalytic mechanism, for first-order kinetics were observed over the entire concentration range with t 1/2 = 4 min at each concentration. However, the percentage of activable C1 decreased with dilution due to C1 dissociation (i.e., C1qr2s2 leads to C1q + C1r2s2). The observed concentration of C1 that spontaneously activated at each dilution equalled the concentration of C1 present as macromolecular C1. When reconstituted C1 was mixed with normal human serum (NHS) and then incubated at 37 degrees C, spontaneous C1 activation was completely inhibited. Pretreating NHS at 56 degrees C for 30 min destroyed its inhibitory activity. In conclusion, C1 spontaneously autoactivates at 37 degrees C by an intramolecular mechanism. This activation is suppressed in NHS.</abstract><cop>Bethesda, MD</cop><pub>Am Assoc Immnol</pub><pmid>6281332</pmid><doi>10.4049/jimmunol.128.6.2500</doi><tpages>5</tpages><oa>free_for_read</oa></addata></record>
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subjects Analysis of the immune response. Humoral and cellular immunity
Benzoates - pharmacology
Biological and medical sciences
Catalysis
Cell interactions
Complement Activating Enzymes
Complement Activation
Complement C1 - metabolism
Complement C1q
Complement C1r
Complement C1s
Fundamental and applied biological sciences. Psychology
Fundamental immunology
Guanidines - pharmacology
Humans
Immunobiology
Kinetics
Macromolecular Substances
Phenylmethylsulfonyl Fluoride - pharmacology
Protease Inhibitors - pharmacology
Temperature
Time Factors
title Spontaneous activation of the first component of human complement (C1) by an intramolecular autocatalytic mechanism
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