Biocatalyst as a core component of an enzyme-catalyzed redox system for the biocatalytic reduction of cystine

An enzyme for reducing cystine to cysteine, wherein the enzyme is a fusion protein that comprises the protein activities of

• i) thioredoxin (protein i) having KEGG database number EC 1.8.4.8 or EC 1.8.4.10, wherein thioredoxin (protein i) is the protein activity of thioredoxin 1 from E. coli, and
• ii) thioredoxin reductase (protein ii) having KEGG database number EC 1.8.1.9, wherein the thioredoxin reductase (protein ii) is the protein activity of the thioredoxin reductase from E. coli,
• wherein the activity of the fusion protein is at least 100% of the activity of a mixture of the same but unfused individual proteins i and ii,
• wherein the fusion protein has the enzyme activity to reduce cystine to cysteine and wherein the coding sequences (cds) responsible for the activity of protein i and ii have been fused.