Method for quantitatively determining homocysteine and a reagent for quantitative determination of homocysteine

1. A method for quantitatively determining homocysteine in a biological specimen containing homocysteine and cysteine by use of an enzyme which is capable of forming hydrogen sulfide both from homocysteine and from cysteine, wherein the enzyme is O-acetyl homoserine lyase or L-methionine γ-lyase which comprises: (a) reacting the biological specimen with cysteine dioxygenase in the absence of a reducing agent, (b) subsequently reacting the resultant specimen of (a) with a reducing agent and the enzyme which is capable of forming hydrogen sulfide both from homocysteine and from cysteine, and (c) measuring the concentration of the hydrogen sulfide thus obtained to determine the homocysteine concentration in the biological specimen.

2. The method for quantitatively determining homocysteine according to claim 1 , wherein the reaction (a) is carried out in a buffer solution with pH of 5.5 to 7.

3. The method for quantitatively determining homocysteine according to claim 1 , wherein the reducing agent is a thiol compound.

4. The method for quantitatively determining homocysteine according to claim 1 , wherein the concentration of the formed hydrogen sulfide is measured with metal ions and a metal indicator.

5. The method for quantitatively determining homocysteine according to claim 1 , wherein the cysteine dioxygenase is stored in a buffer solution with pH of 5.5 to 7 before the reaction (a).

6. The method for quantitatively determining homocysteine according to claim 1 , wherein the cysteine dioxygenase is cryopreserved in a buffer solution with pH of 5.5 to 7 containing sodium chloride or ammonium sulfate before the reaction (a).

7. The method for quantitatively determining homocysteine according to claim 1 , wherein the cysteine dioxygenase is lyophilized in a buffer solution with pH of 5.5 to 7 containing sodium chloride or ammonium sulfate and a sugar, in which cysteine dioxygenase is dissolved, before the reaction (a).

8. A reagent for quantitative determination of homocysteine, which comprises a reagent (I) containing cysteine dioxygenase, a reagent (II) containing a reducing agent and an enzyme which is capable of forming hydrogen sulfide both from homocysteine and from cysteine, wherein the enzyme is O-acetyl homoserine lyase or L-methionine γ-lyase and a reagent (III) containing metal ions and a metal indicator.

9. The reagent for quantitative determination of homocysteine according to claim 8 , wherein the reducing agent is a thiol compound.

10. The reagent for quantitative determination of homocysteine according to claim 8 , wherein the reagent (I) is obtained by dissolving cysteine dioxygenase in a buffer solution with pH of 5.5 to 7.

11. The reagent for quantitative determination of homocysteine according to claim 8 , wherein the reagent (I) is obtained by dissolving cysteine dioxygenase in a buffer solution with pH of 5.5 to 7 containing sodium chloride or ammonium sulfate, and cryopreserving it.

12. The reagent for quantitative determination of homocysteine according to claim 8 , wherein the reagent (I) is obtained by dissolving cysteine dioxygenase in a buffer solution with pH of 5.5 to 7 containing sodium chloride or ammonium sulfate and a sugar, and lyophilizing it.

13. The reagent for quantitative determination of homocysteine according to claim 8 , wherein the enzyme is O-acetyl homoserine-lyase.

14. The reagent for quantitative determination of homocysteine according to claim 8 , wherein the enzyme is L-methionine γ-lyase.

15. The method for quantitative determination of homocysteine according to claim 1 , wherein the enzyme is O-acetyl homoserine-lyase.

16. The method for quantitative determination of homocysteine according to claim 1 , wherein the enzyme is L-methionine γ-lyase.