HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Rawal, N. Articles by Pangburn, M. K. Search for Related Content PubMed PubMed Citation Articles by Rawal, N. Articles by Pangburn, M. K. Social Bookmarking                      What's this?

J Biol Chem, Vol. 273, Issue 27, 16828-16835, July 3, 1998

C5 Convertase of the Alternative Pathway of Complement
KINETIC ANALYSIS OF THE FREE AND SURFACE-BOUND FORMS OF THE ENZYME

From the Department of Biochemistry, University of Texas Health Science Center, Tyler, Texas 75710

Although proteolytic activation of the complement protein C5 initiates important defensive and occasionally pathological inflammatory reactions, the enzymatic properties of the enzymes responsible for this cleavage have never been examined. We have studied the kinetic parameters of the C5 convertase of the alternative pathway of complement, either bound to a zymosan surface or in its monomeric soluble form. C5 convertase enzymatic activity was measured as a function of C5 concentration by quantitating production of C5b,6 under physiological conditions of temperature, pH, and ionic strength. The C5 convertases appeared to follow Michaelis-Menten kinetics and exhibited similar catalytic rate constants (k_cat). However, the surface-bound enzyme, ZymC3b,Bb had a K_m (1.4 µM) that was 17 times lower than that of the soluble monomeric form of the enzyme, C3b,Bb (K_m = 24 µM). The k_cat for the cell-bound enzyme, ZymC3b,Bb was 0.0048 s¹ and that for soluble C3b,Bb was 0.0110 s¹. Both forms of the enzyme had a low turnover number at V_max (0.23 to 0.68 C5/min/enzyme). Substituting Mg²⁺ for Ni²⁺ did not alter the kinetic parameters but lowered the half-life of the enzyme by 5-7-fold. The kinetic data presented demonstrate that the fluid phase C5 convertase, C3b,Bb, can cleave C5 without the aid of a second C3b molecule. The results also show that the greater enzymatic activity previously observed for the surface-bound C5 convertases is not due to higher catalytic efficiency but is solely due to higher affinity for the substrate C5. In blood, C5 concentrations are 3-4-fold below the K_m determined for the surface-bound C5 convertase suggesting a direct correlation between the local C5 concentration and production of the anaphylatoxin C5a and the cytolytic C5b-9 complex.

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				V. P. Ferreira, A. P. Herbert, C. Cortes, K. A. McKee, B. S. Blaum, S. T. Esswein, D. Uhrin, P. N. Barlow, M. K. Pangburn, and D. Kavanagh The Binding of Factor H to a Complex of Physiological Polyanions and C3b on Cells Is Impaired in Atypical Hemolytic Uremic Syndrome J. Immunol., June 1, 2009; 182(11): 7009 - 7018. [Abstract] [Full Text] [PDF]

				K. J. Katschke Jr., S. Stawicki, J. Yin, M. Steffek, H. Xi, L. Sturgeon, P. E. Hass, K. M. Loyet, L. DeForge, Y. Wu, et al. Structural and Functional Analysis of a C3b-specific Antibody That Selectively Inhibits the Alternative Pathway of Complement J. Biol. Chem., April 17, 2009; 284(16): 10473 - 10479. [Abstract] [Full Text] [PDF]

				N. Rawal, R. Rajagopalan, and V. P. Salvi Activation of Complement Component C5: COMPARISON OF C5 CONVERTASES OF THE LECTIN PATHWAY AND THE CLASSICAL PATHWAY OF COMPLEMENT J. Biol. Chem., March 21, 2008; 283(12): 7853 - 7863. [Abstract] [Full Text] [PDF]

				I. Jongerius, J. Kohl, M. K. Pandey, M. Ruyken, K. P.M. van Kessel, J. A.G. van Strijp, and S. H.M. Rooijakkers Staphylococcal complement evasion by various convertase-blocking molecules J. Exp. Med., October 1, 2007; 204(10): 2461 - 2471. [Abstract] [Full Text] [PDF]

				M. A. Figueira, S. Ram, R. Goldstein, D. W. Hood, E. R. Moxon, and S. I. Pelton Role of Complement in Defense of the Middle Ear Revealed by Restoring the Virulence of Nontypeable Haemophilus influenzae siaB Mutants Infect. Immun., January 1, 2007; 75(1): 325 - 333. [Abstract] [Full Text] [PDF]

				A. Garg, P. F. Barnes, A. Porgador, S. Roy, S. Wu, J. S. Nanda, D. E. Griffith, W. M. Girard, N. Rawal, S. Shetty, et al. Vimentin Expressed on Mycobacterium tuberculosis-Infected Human Monocytes Is Involved in Binding to the NKp46 Receptor J. Immunol., November 1, 2006; 177(9): 6192 - 6198. [Abstract] [Full Text] [PDF]

				V. P. Ferreira, A. P. Herbert, H. G. Hocking, P. N. Barlow, and M. K. Pangburn Critical Role of the C-Terminal Domains of Factor H in Regulating Complement Activation at Cell Surfaces J. Immunol., November 1, 2006; 177(9): 6308 - 6316. [Abstract] [Full Text] [PDF]

				E. Afrimzon, N. Zurgil, Y. Shafran, J. Sandbank, R. Orda, S. Lalchuk, and M. Deutsch Monitoring of Intracellular Enzyme Kinetic Characteristics of Peripheral Mononuclear Cells in Breast Cancer Patients Cancer Epidemiol. Biomarkers Prev., February 1, 2004; 13(2): 235 - 241. [Abstract] [Full Text] [PDF]

				H. U. Lutz, P. Stammler, V. Bianchi, R. M. Trueb, T. Hunziker, R. Burger, E. Jelezarova, and P. J. Spath Intravenously applied IgG stimulates complement attenuation in a complement-dependent autoimmune disease at the amplifying C3 convertase level Blood, January 15, 2004; 103(2): 465 - 472. [Abstract] [Full Text] [PDF]

				N. Rawal and M. K. Pangburn Formation of High Affinity C5 Convertase of the Classical Pathway of Complement J. Biol. Chem., October 3, 2003; 278(40): 38476 - 38483. [Abstract] [Full Text] [PDF]

				N. Rawal and M. K. Pangburn Formation of High-Affinity C5 Convertases of the Alternative Pathway of Complement J. Immunol., February 15, 2001; 166(4): 2635 - 2642. [Abstract] [Full Text] [PDF]

				M. K. Pangburn, K. L. W. Pangburn, V. Koistinen, S. Meri, and A. K. Sharma Molecular Mechanisms of Target Recognition in an Innate Immune System: Interactions Among Factor H, C3b, and Target in the Alternative Pathway of Human Complement ,2 J. Immunol., May 1, 2000; 164(9): 4742 - 4751. [Abstract] [Full Text] [PDF]

				N. Rawal and M. K. Pangburn Functional Role of the Noncatalytic Subunit of Complement C5 Convertase J. Immunol., February 1, 2000; 164(3): 1379 - 1385. [Abstract] [Full Text] [PDF]