CHAPTER IX 



COMPLP^MENT 



Complement. — Definition. — Complement may be defined as a 

 thermolabile enzyme-like colloid, present in the serum of animaLs, 

 that has the ability to combine with sensitized eells and bring about 

 their lysis under suitable conditions. 



The history of the discovery and naming of this su])stance is dis- 

 cussed briefly in an earlier cliapter. It was regarded as an enzyme 

 by Buchner who named it alexin and regarded it as of leucocytic 

 origin. Ehrlicli regarded it as having a combining or haptophore 

 group and a zjnnophore or enzyme-like group which was respon- 

 sible for lysis. Some of its enzyme-like properties may be sum- 

 marized as follows: (1) It is colloidal in nature. (2) The 

 presence of a small amount brings about extensive chemical changes 

 in the substrate (cells). (3) It is thermolabile. (4) The reaction 

 is about as reversible as enzyme reactions. (5) The optimum 

 temperature for its action is 37° C. (6) Antienzymes as well as 

 anticomplcment have been reported. (7) There is considerable evi- 

 dence that its activity is interfered with by the end products of 

 its action. 



Nature of Complement. — Biochemically speaking, Ferrata 

 (1907) reported that complement is composed of an albumin frac- 

 tion, named by Brand (1907) "endpiece," and a globulin frac- 

 tion which he calls "midpiece." Subsequent work by Whitehead, 

 Gordon and Wornall (1925) indicates that the midpiece consists 

 of a heat labile euglobulin fraction and a heat stable fraction named 

 tlic third component. The latter can be removed from a serum by 

 treatment with zymin (residue after acetone and ether extraction 

 of yeast) and restored by adding guinea pig serum heated to 56° C. 



In 1926 the same authors reported that complement could be 

 rendered inactive by treatment with appropriate concentrations 

 of ammonia and that the activity could be restored b\- tlic addition 

 of either heated or zyniin-treated serum. They named this 

 ammonia sensitive fraction the ''fourth" component and de- 

 termined that it is associated with the endpiece. Pillemer, Seifter 



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