The amino acid sequence of the fluorescein-labeled peptides of electric ray and brine shrimp (Na,K)-ATPase.

(Na,K)-ATPase from Torpedo californica (electric ray) and Artemia salina (brine shrimp) was labeled with fluorescein 5'-isothiocyanate (FITC) with concomitant loss of activity. Both inactivation and binding were inhibited in the presence of ATP. The sequence of the peptide resulting from tryptic digest containing labeled lysine from both enzymes is Tyr-Leu-Leu-Val-Met-Lys*-Gly-Ala-Pro-Glu-Arg. Thus the primary structure of this region is shown to be conserved in the enzymes of a nonvertebrate and a vertebrate.