The Importance of SH-Groups for Enzymic Activity. 7. The Amino Acid Sequence around the Essential SH-Group of Pig Heart Lactate Dehydrogenase, Isoenzyme I.

1 The amino acid sequence of a dodecapeptide containing the essential SH-group of pig heart l-lactate dehydrogenase, isoenzyme I, was determined as Val-Ile-Gly-Ser-Gly-Cys-Asn-Leu-Asp-Ser-Ala-Arg. This sequence shows three differences with that of an SH-peptide from chicken LDH-I. 2 It is shown that the possible codons for the amino acids occupying equivalent positions in the heptapeptides around the essential SH-groups of glyceraldehyde 3-phosphate-, yeast alcohol-, liver alcohol- and lactate dehydrogenases can be related to one another by a chain of point mutations.