Fructose amino acid oxidase, preparation method and enzyme-containing kit for detecting glycated albumin
Fructosyl amino acid oxidase is provided, which has an amino acid sequence as shown in SEQID. No. 1 or fructosyl amino acid oxidase having a homology of more than 80% with this amino acid sequence, on a corresponding site of an amino acid selected from following (a) to (f), having one or more amino acid residues conducting a substitution, obtained fructosyl amino acid oxidase having a higher thermostability: (a) 59-site glutamic acid, (b) 98-site glutamic acid, (c) 225-site glycine, (d) 277-site lysine, (e) 285-site glutamic acid, and (f) 355-site aspartic acid. The method for preparing the above oxidase and the test kit containing the enzyme for determining glycated albumin are also provided.
1. A fructosyl amino acid oxidase comprising the amino acid sequence of SEQ ID No: 1, wherein glutamic acid at position 59 of SEQ ID No: 1 is substituted with an amino acid selected from the group consisting of L, I, V, F, M, W, T, C, N, Y, D, and H, and wherein the fructosyl amino acid exhibits a higher thermostability compared to the fructosyl amino acid oxidase of SEQ ID No: 1.
2. A fructosyl amino acid oxidase comprising the amino acid sequence of SEQ ID No: 1, wherein glutamic acid at position 59 of SEQ ID No: 1 is substituted with phenylalanine (F), wherein the fructosyl amino acid oxidase further comprises an additional substitution to SEQ ID No: 1 selected from the group consisting of substitutions (a) to (k), wherein the fructosyl amino acid exhibits a higher thermostability compared to the fructosyl amino acid oxidase of SEQ ID No: 1, and wherein the substitutions (a) to (k) are as follows:
(a) E98C
(b) G225D
(c) K227N
(d) E285F
(e) E98C and G225F
(f) G225D and K227N
(g) K227N and E285I
(h) E98C, G225F, and K277N
(i) G225D, K277N, and E285F
(j) E98C, G225F, K277N, and E285F
(k) E98C, G225F, K227N, E285F, and D355L.
3. A polynucleotide encoding the fructosyl amino acid oxidase of claim 1 .
4. A test kit for determining glycated albumin, the kit comprising a reagent 1 and reagent 2, wherein reagent 1 comprises 20-200 mM buffer, 10-100 KU/L protease, 10-100 KU/L peroxidase, 5-50 mM 4-amino-antipyrine, and 0.01 to 0.05% preservative, and wherein reagent 2 comprises 20-200 mM buffer, 10-100 KU/L of the fructosyl amino acid oxidase of claim 1 , 1-10 mM chromogen, and 0.01 to 0.05% preservative.
5. The test kit of claim 4 , wherein the buffer is selected from the group consisting of tris-hydrochloride buffer, acetic acid-sodium acetate buffer, phthalic-acid-hydrochloric acid buffer, and glycine-hydrochloric acid buffer.
6. The test kit of claim 4 , wherein the protease is selected from the group consisting of trypsin, basophilic protease, proteinase A, and proteinase K.
7. The test kit of claim 4 , wherein chromogen is selected from the group consisting of N, N-di(4-sulfobutyl)-3-methylaniline disodium salt, N-ethyl-N-(3-sulfopropyl)-3-methylaniline sodium salt, and N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3-methylaniline sodium salt.
8. The test kit of claim 4 , wherein the preservative is 2-methyl-4-isothiazolin-3-one.