When equal amounts of extrorotatory and levorotatory isomers are present, the resulting mixture becomes optically inactive because the optical activities of each isomer cancel each other.

Such a mixture is called a racemic or dl-mixture or (±)-conglomerate and this process of converting an optically active compound into the racemic modification is known of racemization. 

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#Id: 4669

#Unit 13. Methods in Biology

The bacterium Streptococcus pyogenes, for example, expresses cell-wall proteins called M antigens. Antibodies produced to streptococcal M antigens have been shown to cross-react with several myocardial and skeletal muscle proteins and have been implicated in heart and kidney damage following streptococcal infections. 

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#Id: 4670

#Unit 13. Methods in Biology

Glycosphingolipids as determinants of blood groups

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#Id: 4671

#Unit 13. Methods in Biology

Antibody and soluble antigen interacting in aqueous solution form a lattice that eventually develops into a visible precipitate. Antibodies that aggregate soluble antigens are called precipitins.

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#Id: 4672

#Unit 13. Methods in Biology

A precipitation curve for a system of one antigen and its antibodies. This plot of the amount of antibody precipitated versus increasing antigen concentrations (at constant total antibody) reveals three zones: 

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#Id: 4673

#Unit 13. Methods in Biology

A related quantitative technique, rocket electrophoresis, does permit measurement of antigen levels. In rocket electrophoresis, a negatively charged antigen is electrophoresed in a gel containing antibody. The precipitate formed between antigen and antibody has the shape of a rocket, the height of which is proportional to the concentration of antigen in the well. 

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#Id: 4674

#Unit 13. Methods in Biology

One limitation of rocket electrophoresis is the need for the antigen to be negatively charged for electrophoretic movement within the agar matrix