The importance of SH-groups for enzymic activity. IV. Preparation of the tryptic peptides containing the essential cysteine residues of lactate dehydrogenase, isozymes I and V
Holbrook, J.J.; Pfleiderer, G.; Schnetger, J.; Diemair, S.
Biochem Z 344(1): 1-14
The reactions of 13 N-substituted maleinimides with the essential sulfhydryl groups of lactate dehydrogenase (LDH, EC 22.214.171.124) and glyceraldehyde-3-phosphate dehydrogenase (EC 126.96.36.199) are described. The smaller maleinimides reacted much more rapidly than the larger ones. N-(gamma-Phenylbutyl)-and the N-(4-sulphamoylphenyl)-maleinimides had higher reactivities than was expected from their size alone. The essential SH-groups of pig LDH.I and all the SH-groups of LDH-V were labeled with N-(N-acetyl-4-[35S]-sulphamoylphenyl)-maleinimide (ASPM). One of the ASPM-labelled tryptic peptides of LDH-V was shown to have the same amino acid analysis as the essential cysteine peptide of LDH-L The partial sequence of the ASPM-peptide of pig LDH-I is Val-Ile-(Gly, Ser)-(Asp2, ASPM-Cys, Gly, Ser)-(Ala, Leu)-Arg. The structure of this peptide is compared with that of the beef heart LDH peptide described by other workers.