Method of assaying glycated protein
The present invention provides a convenient, efficient method for assaying glycated protein, fructosyl peptide, or fructosyl amino acid which can be performed with reduced effect of fructosyl lysine compounds. The invention also provides a reagent for the assay. The invention is directed to a method for reducing the effect of a fructosyl lysine compound in an assay of fructosyl peptide or fructosyl amino acid contained in a sample, characterized by including causing an enzyme for assaying fructosyl peptide or fructosyl amino acid to act specifically on fructosyl peptide or fructosyl amino acid at a pH of 4.0 to 7.0 and measuring the product at a pH of 4.0 to 7.0; and a method for assaying glycated protein through the above method.
1. A method for reducing the effect of a fructosyl lysine compound in an assay of a glycated protein-containing sample, the method comprising
treating the sample with a protease to release free fructosyl valine or fructosyl valylhistidine,
reacting a fructosyl peptide oxidase with the released fructosyl valine or fructosyl valylhistidine in the sample at a pH of 4.0 to 7.0 to produce hydrogen peroxide thereby reducing the effect of fructosyl lysine compound in the assay,
measuring the hydrogen peroxide at a pH of 4.0 to 7.0; and
correlating the measuring of the hydrogen peroxide to the presence or level of glycated protein in the sample.
2. A method according to claim 1 , wherein the glycated protein is a glycated hemoglobin.
3. The method of claim 1 or 2 , wherein the protease is obtained from:
(a) a microorganism belonging to a genus selected from the group consisting of Bacillus, Aspergillus , and Streptomyces , or
(b) a gene of the microorganism of (a) through a gene recombination technology.
4. The method of claim 1 , wherein the enzyme for assaying fructosyl valine or fructosyl valylhistidine is a fructosyl peptide oxidase.
5. A reagent for assaying glycated protein with reduced effect of a fructosyl lysine compound, which comprises:
(A) a protease;
(B) an oxidase which specifically acts on fructosyl valine or fructosyl valylhistidine at a pH of 4.0 to 7.0 to thereby produce hydrogen peroxide; and
(C) a reagent for measuring hydrogen peroxide.
6. A method for reducing the effect of a fructosyl lysine compound in an assay of fructosyl valine or fructosyl valylhistidine in a sample, the method comprising:
reacting at least one of the following (A) to (C) with free fructosyl valine or fructosyl valylhistidine at a pH of 4.0 to 7.0 after the sample has been reacted with a protease to release free fructosyl valine or fructosyl valylhistidine; and recovering a product resulting from the action of (A) to (C) in the presence or absence of fructosyl valine or fructosyl valylhistidine in the sample
(A) a fructosyl peptide oxidase,
(B) a reagent for measuring hydrogen peroxide, and
(C) a glucosone-oxidizing and decomposing enzyme.
7. A method for reducing the effect of a fructosyl lysine compound in an assay of glycated protein contained in a sample, comprising: treating the sample with a protease to thereby release fructosyl valine or fructosyl valylhistidine;
reacting a fructosyl peptide oxidase, a reagent for measuring hydrogen peroxide, or a glucosone-oxidizing and decomposing enzyme with released fructosyl valine or fructosyl valylhistidine at a pH of 4.0 to 7.0 in the presence or absence of a glycated protein in the sample.
8. The method of claim 7 , wherein the glycated protein is a glycated hemoglobin.
9. The method of claim 7 or 8 , wherein the protease is obtained from (A) a microorganism belonging to a genus selected from the group consisting of Bacillus, Aspergillus , and Streptomyces , or (B) is obtained from a gene of the microorganism of (A) through a gene recombination technology.
10. The method of claim 6 or 7 , wherein the enzyme for assaying fructosyl valine or fructosyl valylhistidine is a fructosyl peptide oxidase.