Abstract: The present invention provides a stabilizer that can stabilize a salt of 10-(carboxymethylaminocarbonyl)-3,7-bis(dimethylamino)phenothiazine or a derivative thereof even under the existence of moisture or under light irradiation. A compound described in at least one of (1) and (2) below is used as the stabilizer of the salt of 10-(carboxymethylaminocarbonyl)-3,7-bis(dimethylamino)phenothiazine or the derivative thereof.

Abstract: The present invention provides a phenothiazine-derivative color-measuring method that can detect a phenothiazine-derivative color even at a wavelength longer than the wavelength that exhibits maximum absorption.

Abstract: A method of measuring HbA1c is provided that, even with a whole blood sample after storage, measurement accuracy substantially equal to a whole blood sample right after collection can be maintained. Whole blood is stored in a presence of a glycolytic inhibitor and protease is added to the stored whole blood sample to cleave hemoglobin in the whole blood sample. Then a glycated part of a hemoglobin fragment thereby obtained is treated with fructosyl amine oxidase. Thereafter, a glycation degree of HbA1c is determined by measuring a redox reaction between the glycated part and the fructosyl amine oxidase. Further, instead of storage of the whole blood in a presence of the glycolytic inhibitor, a strong electrolyte substance such as KCl, K2SO4, KNO, NaCl, Na2SO4, NaNO, MgCl2, MgSO4, Mg(NO)2, etc. is added to the whole blood after storage and a protease treatment is performed in a presence of the strong electrolyte substance.

Abstract: The present invention provides a stabilizer that can stabilize a salt of 10-(carboxymethylaminocarbonyn-3,7-bis(dimethylamino)phenothiazine or a derivative thereof even under the existence of moisture or under light irradiation. A compound described in at least one of (1) and (2) below is used as the stabilizer of the salt of 10-(carboxymethylaminocarbonyl)-3,7-bis(dimethylamino)phenothiazine or the derivative thereof.

Abstract: A liquid reagent in which a methylene blue compound color former is stably stored in a liquid state; and a method of stabilizing a methylene blue compound color former in a liquid state. A methylene blue compound color former is stabilized by causing it to coexist with either a quaternary ammonium compound having a C12 or higher hydrocarbon chain or a salt thereof in a liquid medium. Examples of the methylene blue compound color former include 10-(carboxymethylaminocarbonyl)-3,7-bis(dimethylamino) phenothiazine.

Abstract: The present invention provides a method for cleaving a glycated protein to obtain an amino acid or a peptide efficiently with a protease. By treating the glycated protein with the protease in the presence of a compound represented by R—X, the amino acid or the peptide is obtained by the cleavage. The R represents an alkyl compound with a carbon number of 9 or more, and preferably is straight-chain alkyl or straight-chain acyl with a carbon number of 9 to 16, branched-chain alkyl or branched-chain acyl with a carbon number of 10 to 40 and a main-chain carbon number of 9 to 16, or straight-chain alkyl that is substituted by cycloalkyl (a carbon number of the cycloalkyl ranges from 3 to 8, and a carbon number of the straight chain ranges from 4 to 13), where X is a sugar residue. Moreover, the glycated protein is, for example, glycated hemoglobin, and preferably ?-chain N-terminal amino acid or a ?-chain N-terminal peptide is cleaved by the protease treatment.

Abstract: A method of measuring HbA1c is provided that, even with a whole blood sample after storage, measurement accuracy substantially equal to a whole blood sample right after collection can be maintained. Whole blood is stored in a presence of a glycolytic inhibitor and protease is added to the stored whole blood sample to cleave hemoglobin in the whole blood sample. Then a glycated part of a hemoglobin fragment thereby obtained is treated with fructosyl amine oxidase. Thereafter, a glycation degree of HbA1c is determined by measuring a redox reaction between the glycated part and the fructosyl amine oxidase. Further, instead of storage of the whole blood in a presence of the glycolytic inhibitor, a strong electrolyte substance such as KCl, K2SO4, KNO, NaCl, Na2SO4, NaNO, MgCl2, MgSO4, Mg(NO)2, etc. is added to the whole blood after storage and a protease treatment is performed in a presence of the strong electrolyte substance.

Abstract: The present invention provides a phenothiazine-derivative color-measuring method that can detect a phenothiazine-derivative color even at a wavelength longer than the wavelength that exhibits maximum absorption.

Abstract: The present invention provides a method for cleaving a glycated protein to obtain an amino acid or a peptide efficiently with a protease. By treating the glycated protein with the protease in the presence of a compound represented by R—X, the amino acid or the peptide is obtained by the cleavage. The R represents an alkyl compound with a carbon number of 9 or more, and preferably is straight-chain alkyl or straight-chain acyl with a carbon number of 9 to 16, branched-chain alkyl or branched-chain acyl with a carbon number of 10 to 40 and a main-chain carbon number of 9 to 16, or straight-chain alkyl that is substituted by cycloalkyl (a carbon number of the cycloalkyl ranges from 3 to 8, and a carbon number of the straight chain ranges from 4 to 13), where X is a sugar residue. Moreover, the glycated protein is, for example, glycated hemoglobin, and preferably ?-chain N-terminal amino acid or a ?-chain N-terminal peptide is cleaved by the protease treatment.

Abstract: A liquid reagent in which a methylene blue compound color former is stably stored in a liquid state; and a method of stabilizing a methylene blue compound color former in a liquid state. A methylene blue compound color former is stabilized by causing it to coexist with either a quaternary ammonium compound having a C12 or higher hydrocarbon chain or a salt thereof in a liquid medium. Examples of the methylene blue compound color former include 10-(carboxymethylaminocarbonyl)-3,7-bis(dimethylamino) phenothiazine.