David L. Haviland, Ph.D. dhavilan at IMM2.IMM.UTH.TMC.EDU
Fri Jan 3 11:14:47 EST 1997

At 16:45 1/2/97 -0800, Kenneth T. Miyasaki DDS PhD wrote:
>Complement (C) is a component of the immune system formed by an
>interacting network of plasma glycoproteins and cell receptors. The

Though noble, you have saved the individual who posed the question the
library time he needed to answer the question himself... ;-)

>Components of the 
>Membrane Attack Complex
>	C5 (encoded on chromosome 9q34.1) is a 191 kdal heterodimeric protein
>consisting of one115 kdal and one 75 kdal subunit. Cleavage of the
>larger subunit by the C5 convertase results in the formation of a 11.2
>kdal C5a chemoattractant molecule and 180 kdal C5b. C5 is structurally
>related to C3 and C4, and has the internal thioester bond that dominates
>the behavior of these molecules.

As Ken obtained and posted this summary of complement, he is not the
author, so I do not blame him for errors in this article.  I do, however,
suggest the author, whomever that may be, revise this summary.  

True, C3,C4, & C5 are conserved in amino acid sequences and share similar
gene structural organization.  However, the last sentence is simply wrong,
plain and simple.   C5 *never* did, nor does it currently have a thioester
bond.  The future is up to evolution.  Only C3 and C4  (and
alpha-2-macroglobulin) possess this unique chemistry.  C5 does have the
critical Cys residue for thioester bond formation, while a2M, C3, and  C4 do.


 David L. Haviland, Ph.D.
 Asst. Prof. Immunology 
 University of Texas - Houston, H.S.C.
 Institute of Molecular Medicine  
 2121 W. Holcombe Blvd.  
 Houston, TX  77030 
 Internet:"dhavilan at" 
 Voice: 713.500.2413  FAX: 713.500.2424
" Sometimes you're the windsheild, sometimes you're the bug."

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