4.2.1.96 C81R mutant enzyme Cys81Arg has significantly lower activity 5932 4.2.1.96 C82R mutant enzyme C82R reveals 60% decrease in Vmax and a slight decrease in Km-value for 4a-hydroxytetrahydrobiopterin. The susceptibility to proteolysis of mutant C82R, however is markedly increased compared with the wild type enzyme 5936 4.2.1.96 C82R mutant enzyme expressed as a soluble form has 40% of normal activity 668883 4.2.1.96 D100N the single mutants H73A and H74A and the double mutant H73A,H74A are completely inactive. The activity of the mutant enzymes H91A and E69A is 40% of the activity of the wild type enzyme. The activity of the mutant enzymes D100N is 10% of the activity of the wild type enzyme 5929 4.2.1.96 E57A the His79Ala mutant and the His79Ser mutant exhibit about 40% the activity of the wild-type enzyme. In the mutant enzymes His61Ala and His62Ala the activity is reduced to 10%. In the mutant enzymes Asp60Ala and Arg87Ala the activity is reduced to 30%. The Glu57Ala mutant and the His61Ala,His62Ala double mutant show no activity 5933 4.2.1.96 E69A the single mutants H73A and H74A and the double mutant H73A,H74A are completely inactive. The activity of the mutant enzymes H91A and E69A is 40% of the activity of the wild type enzyme. The activity of the mutant enzymes D100N is 10% of the activity of the wild type enzyme 5929 4.2.1.96 E97K a biopsy of duodenal mucosa from a patient with homozygous E97K mutation has 17% of normal activity 668883 4.2.1.96 H61A mutant enzyme H61A shows no dehydratase activity with 4a(R)-hydroxy-6(R)-methyltetrahydropterin. Mutant enzyme H79A shows no dehydratase activity with 4a(S)-hydroxy-6(R)-methyltetrahydropterin. The Km-value for 4a(S)-hydroxy-6(R)-methyltetrahydropterin is comparable to the Km-value of the wild type enzyme. The turnover number of the mutant enzyme H62A is 24% of that with the wild type enzyme for the 4a(R),6(S)-isomer and the 4a(S),6(R)-isomer 5940 4.2.1.96 H61A the His79Ala mutant and the His79Ser mutant exhibit about 40% the activity of the wild-type enzyme. In the mutant enzymes His61Ala and His62Ala the activity is reduced to 10%. In the mutant enzymes Asp60Ala and Arg87Ala the activity is reduced to 30%. The Glu57Ala mutant and the His61Ala,His62Ala double mutant show no activity 5933 4.2.1.96 H61A/H62A the His79Ala mutant and the His79Ser mutant exhibit about 40% the activity of the wild-type enzyme. In the mutant enzymes His61Ala and His62Ala the activity is reduced to 10%. In the mutant enzymes Asp60Ala and Arg87Ala the activity is reduced to 30%. The Glu57Ala mutant and the His61Ala,His62Ala double mutant show no activity 5933