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406 Kruger<br />

Table 1<br />

Variation in Species Specificity<br />

of Various Immunogobulin-Binding <strong>Protein</strong>s<br />

Immunoglobulin<br />

Affinity of binding by<br />

Species class <strong>Protein</strong> A <strong>Protein</strong> G <strong>Protein</strong> L <strong>Protein</strong> LA<br />

Human IgG1 a +++ +++ +++ +++<br />

IgG2 +++ +++ +++ +++<br />

IgG3 – +++ +++ +++<br />

IgG4 +++ +++ +++ +++<br />

IgM – – +++ +++<br />

IgA – – +++ +++<br />

IgE – – +++ +++<br />

IgD – – +++ +++<br />

Mouse IgG1 a + +++ +++ +++<br />

IgG2a +++ +++ +++ +++<br />

IgG2b ++ ++ +++ +++<br />

IgG3 + ++ +++ +++<br />

Rat IgG1 – + +++ +++<br />

IgG2a – +++ +++ +++<br />

IgG2b – ++ +++ +++<br />

IgG2c + ++ +++ +++<br />

Cow IgG ++ +++ – ++<br />

Cat IgG +++ – n.d. n.d.<br />

Chicken IgG – + ++ ++<br />

Dog IgG +++ +++ + ++<br />

Goat IgG +/– ++ – +/–<br />

Guinea pig IgG +++ ++ ++ +++<br />

Hamster IgG + ++ +++ +++<br />

Horse IgG ++ +++ +/– ++<br />

Pig IgG ++ ++ +++ +++<br />

Rabbit IgG +++ ++ + +++<br />

Sheep IgG +/– ++ – +/–<br />

The binding affinities for immunoglobins from different sources is indicated as follows: –,<br />

no binding; +, low; ++, moderate; +++, high; n.d., not determined.<br />

a Denotes major subclass of IgG.<br />

Based on data in refs. 4,8–10 and references therein.<br />

using a second antibody raised against IgG (or other class of immunoglobulin) from<br />

the species used to generate the primary antibody. The advantage of such secondary<br />

antibody systems is that they bind only to antibodies from an individual species. When<br />

combined with different marker enzymes, the specificity of secondary antibodies may<br />

be exploited to identify multiple polypeptides on a single nitrocellulose membrane (4,6).<br />

The marker enzymes most commonly used for detection are alkaline phosphatase<br />

and horseradish peroxidase. Both enzymes can be linked efficiently to other proteins,<br />

such as antibodies, protein A, and avidin, without interfering with the function of the<br />

latter proteins or inactivating the enzyme. Moreover, a broad range of synthetic substrates<br />

have been developed for each of these enzymes. Enzyme activity is normally visualized

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