Mutation library for the identification or generation of SLC41A1 variants, wherein the protein SLC41A1 having the amino acid sequence of SEQ ID NO 1 is the cellular Na + /Mg 2+ exchanger, comprising i) proteins with mutations of SEQ ID NO 1, wherein one of the amino acids of SEQ ID NO 1 is substituted at positions 21 (S>N), 25 (S>Q), 73 (S>N), 76 (S>N), 80 (S>N), 89 (S>N), 97 (S>N), 158 (S>N), 309 (S>N), 394 (S>N), 408 (S>Q), 81 (T>Q), 168 (T>Q), 509 (T>Q) or 278 (Y>N) and proteins with at least one mutation of SEQ ID NO 1, wherein a plurality of these substitutions is present; wherein the mutation library consists of 15 peptides with a single aa mutation and at least one peptide wherein a plurality of these substitutions is present or ii) proteins with mutations of the transmembrane domains and N-, C- termini mutants of SEQ ID NO 1, wherein the amino acids 2-30, 31-60, 61-90, 2-60, 2-90 or 504-513 of SEQ ID NO 1 are deleted (6 mutated proteins) and proteins with mutations of SEQ ID NO 1 in membrane spanning domains, wherein the amino acids 96-205, 225-279, 286-337, 348-427 or 439-503 are deleted (5 mutated proteins) and proteins with mutations in membrane spanning domains of SEQ ID NO 1, wherein the amino acids 99-150, 180-241, 256-306, 317-368, 408-459 or 437-503 are deleted (6 mutated proteins); wherein the mutation library consists of 17 peptides or iii) proteins with leucine zipper mutations of SEQ ID NO 1, wherein the amino acids 482-503 are deleted and wherein amino acids in LZ domain in positions 482 (L>V), 489 (L>V), 494 (L>V), 496 (L>V), 501 (L>V) or 503 (L>V) are substituted; wherein the mutation library consists of 7 peptides or iv) proteins with external loop mutations of SEQ ID NO 1, wherein the amino acids 128-179, 247-254, 310-315, 369-405, or 468-478 are deleted; wherein the mutation library consists of 5 peptides. i) proteins with mutations of SEQ ID NO 1, wherein one of the amino acids of SEQ ID NO 1 is substituted at positions 21 (S>N), 25 (S>Q), 73 (S>N), 76 (S>N), 80 (S>N), 89 (S>N), 97 (S>N), 158 (S>N), 309 (S>N), 394 (S>N), 408 (S>Q), 81 (T>Q), 168 (T>Q), 509 (T>Q) or 278 (Y>N) and proteins with at least one mutation of SEQ ID NO 1, wherein a plurality of these substitutions is present; wherein the mutation library consists of 15 peptides with a single aa mutation and at least one peptide wherein a plurality of these substitutions is present or ii) proteins with mutations of the transmembrane domains and N-, C- termini mutants of SEQ ID NO 1, wherein the amino acids 2-30, 31-60, 61-90, 2-60, 2-90 or 504-513 of SEQ ID NO 1 are deleted (6 mutated proteins) and proteins with mutations of SEQ ID NO 1 in membrane spanning domains, wherein the amino acids 96-205, 225-279, 286-337, 348-427 or 439-503 are deleted (5 mutated proteins) and proteins with mutations in membrane spanning domains of SEQ ID NO 1, wherein the amino acids 99-150, 180-241, 256-306, 317-368, 408-459 or 437-503 are deleted (6 mutated proteins); wherein the mutation library consists of 17 peptides or iii) proteins with leucine zipper mutations of SEQ ID NO 1, wherein the amino acids 482-503 are deleted and wherein amino acids in LZ domain in positions 482 (L>V), 489 (L>V), 494 (L>V), 496 (L>V), 501 (L>V) or 503 (L>V) are substituted; wherein the mutation library consists of 7 peptides or iv) proteins with external loop mutations of SEQ ID NO 1, wherein the amino acids 128-179, 247-254, 310-315, 369-405, or 468-478 are deleted; wherein the mutation library consists of 5 peptides.