Mutants of leucine dehydrogenase sequences, formate dehydrogenase sequences and galactose oxidase sequences are provided. An amino acid sequence that is a mutant of a leucine dehydrogenase sequence as described in SEQ ID 2, or its substantial equivalent, contains at least one mutation selected from the group consisting of F102S, V33A, S351T, N145S and like mutations in subsantially equivalent sequences. An amino acid sequence that is a mutant of a formate dehydrogenase sequence as described in SEQ ID 1, or its substantial equivalent, contains at least one mutation selected from the group consisting of D195S, Y196H, K356T and like mutations in subsantially equivalent sequences. An amino acid sequence that is a mutant of a galactose oxidase sequence as described in SEQ ID 3, or its substantial equivalent, contains at least one mutation selected from the group consisting of N25Y, T94A, D216N, R217C, M278T, Y329C, Q406R, Q406L, V492A, V494A, N521S, N535D, T5491, S567T, T578S and like mutations in subsantially equivalent sequences. Deoxyribonucleic acid molecules containing DNA sequences encoding these mutants are also provided.