Fluorescence assay for kinase activity

1. A method for detecting kinase activity, comprising the steps of:

(a) providing a peptide comprising:

(1) a kinase recognition sequence containing a phosphorylation site;

(2) a β-turn sequence; and

(3) an amino acid of the formula (I):

where each R is independently hydrogen or —SO 2 X, wherein at

least one R group is —SO 2 X, where X is —OR″ or —NR″R′″;

R′ is hydroxy, amino, or thiol;

R″ is C 1-6 alkyl;

R′″ is hydrogen or alkyl; and

n is 1, 2 or 3;

(b) contacting the peptide with a sample comprising Mg 2+ , a phosphate source, and a kinase; and

(c) analyzing for the presence of a phosphorylated peptide product.

2. The method of claim 1 , wherein the amino acid is of the formula (II):

where X is —OR″ or —NR″R′″;

R″ is C 1-6 alkyl; and

R′″ is hydrogen or C 1-6 alkyl.

3. The method of claim 1 , wherein the amino acid is of the formula (III):

4. The method of claim 1 , wherein fluorescence of the peptide increases by at least about 100% when bound to Mg 2+ .

5. The method of claim 1 , wherein the K m of the peptide for the kinase is in the micromolar range.