NOVELTY - A polypeptide with improved affinity for glucose-6-phosphate dehydrogenase, is new. The polypeptide is chosen from e.g. (i) polypeptide comprising a 494 amino acid sequence of SEQ ID NO: 4, in which amino acid at position 46 is substituted by one of amino acid chosen from threonine, cysteine, asparagine, glutamic acid, aspartic acid, serine, glutamine, lysine, valine, isoleucine and glycine.    USE - The polypeptide is useful for producing heat resistance glucose-6-phosphate dehydrogenase (claimed), which is useful for diagnosis, and as fuel cell.    ADVANTAGE - The polypeptide enables to perform an enzyme reaction in cost-effective manner and reduce usage-amount of expensive NAD.    DETAILED DESCRIPTION - A polypeptide with improved affinity for glucose-6-phosphate dehydrogenase, is new. The polypeptide is chosen from (a) (i) polypeptide comprising a 494 amino acid sequence of SEQ ID NO: 4, in which amino acid at position 46 is substituted by one of amino acid chosen from threonine, cysteine, asparagine, glutamic acid, aspartic acid, serine, glutamine, lysine, valine, isoleucine and glycine, (ii) polypeptide comprising an amino acid sequence of SEQ ID NO: 4, in which other than amino acids at position 46 is substituted by one or more amino acids chosen from threonine, cysteine, asparagine, glutamic acid, aspartic acid, serine, glutamine, lysine, valine, isoleucine and glycine, where the polypeptide having glucose-6-phosphate dehydrogenase activity for coenzyme NAD compared to glucose-6-phosphate dehydrogenase, and (iii) polypeptide comprising amino acid sequence exhibiting at least 80% sequence identity to an amino acid sequence of SEQ ID NO: 4, in which other than amino acids at position 46 is substituted by one of amino acid chosen from threonine, cysteine, asparagine, glutamic acid, aspartic acid, serine, glutamine, lysine, valine, isoleucine and glycine, (b) (i) polypeptide comprising amino acid sequence of SEQ ID NO: 4, in which amino acid at position 46 is substituted by threonine, (ii) polypeptide comprising an amino acid sequence of SEQ ID NO: 4, in which other than amino acids at position 46 is substituted by threonine, where the polypeptide having glucose-6-phosphate dehydrogenase activity for coenzyme NAD compared to glucose-6-phosphate dehydrogenase, and (iii) polypeptide comprising amino acid sequence exhibiting at least 80% sequence identity to an amino acid sequence of SEQ ID NO: 4, in which other than amino acids at position 46 is substituted by threonine, (c) (i) polypeptide comprising amino acid sequence of SEQ ID NO: 4, in which amino acid at position 46 is substituted by cysteine, (ii) polypeptide comprising an amino acid sequence of SEQ ID NO: 4, in which other than amino acids at position 46 is substituted by cysteine, where the polypeptide having glucose-6-phosphate dehydrogenase activity for coenzyme NAD compared to glucose-6-phosphate dehydrogenase, and (iii) polypeptide comprising amino acid sequence exhibiting at least 80% sequence identity to an amino acid sequence of SEQ ID NO: 4, in which other than amino acids at position 46 is substituted by cysteine, or (d) (i) polypeptide comprising amino acid sequence of SEQ ID NO: 4, in which amino acid at position 46 is substituted by asparagine, (ii) polypeptide comprising an amino acid sequence of SEQ ID NO: 4, in which other than amino acids at position 46 is substituted by asparagine, where the polypeptide having glucose-6-phosphate dehydrogenase activity for coenzyme NAD compared to glucose-6-phosphate dehydrogenase, and (iii) polypeptide comprising amino acid sequence exhibiting at least 80% sequence identity to an amino acid sequence of SEQ ID NO: 4, in which other than amino acids at position 46 is substituted by asparagines. INDEPENDENT CLAIMS are included for the following:    (1) DNA encoding the above-mentioned polypeptide;    (2) recombinant vector comprising the above-mentioned DNA;    (3) transformant obtained by transforming the recombinant vector into host; and    (4) method for producing the polypeptide.