Tyrosine Kinase in a Nutshell...

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What is Tyrosine Kinase?
A tyrosine kinase is an enzyme that can transfer a phosphate group to a tyrosine residue in a protein, an example of a protein kinase. This is an important function in signal transduction to regulate enzyme activity. A protein kinase is an enzyme that can transfer a phosphate group from a donor molecule (usually ATP) to an amino acid residue of a protein. Enzymes that transfer phosphate groups are known as kinases. The protein kinase mechanism is used in signal transduction for the regulation of enzymes: phosphorylation can activate (or inhibit) the activity of an enzyme. Although most protein kinases are specialized for a single kind of amino acid residue, some exhibit dual kinase activity (they can phosphorylate two different kinds of amino acid).

Tyrosine Kinase Related Diseases
Tyrosine kinases are central protein in regulating cell growth and proliferation. The properly controlled activation of protein tyrosine kinase is essential for normal cell growth and proliferation, constitutive activation of the kinases can contribute to tumor formation. Hence, when the catalytic activity becomes irregular, cancer has a high probability of occurring.  This is especially observed when c-src is over expressed in certain types of cancer (see PubMed Abstracts section on the main page), namely, breast and prostrate cancer.

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Image taken from Rose Richardson, Life Sciences Dept., Bellevue Community College