Patent ID: 8759021

Claim:
A method of quantifying homocysteine in a sample by using first and second methionine auxotrophic mutants of Escherichia coli , the method comprising: measuring the content of homocysteine and methionine in the sample by culturing a first methionine auxotrophic mutant of Escherichia coli in the sample, wherein the first methionine auxotrophic mutant of Escherichia coli is a homocysteine and methionine auxotrophic mutant, measuring the content of methionine in the sample by culturing a second methionine auxotrophic mutant of Escherichia coli in the sample, wherein the second methionine auxotrophic mutant of Escherichia coli is a methionine auxotrophic mutant, and determining the content of homocysteine by subtracting the content of methionine from the content of homocysteine and methionine in the sample, wherein the first and second methionine auxotrophic mutants of Escherichia coli each further comprise a gene encoding luciferase or a fluorescent protein, wherein the expression of the luciferase or the fluorescent protein is in proportion to the growth of the first and second methionine auxotrophic mutants of Escherichia coli , and wherein the content of homocysteine and methionine and the content of methionine are measured from the amount of expression of the luciferase or the fluorescent protein in the first and second methionine auxotrophic mutants of Escherichia coli , respectively.