Nucleoside diphosphate kinase of halobacteria

Nucleotide diphosphate kinase (NDK) was purified from 12 strains of halobacteria using ATP-agarose chromatography and their N-terminal amino acid sequences were determined. The electrophoretic mobilities of these enzymes differed significantly on the native-PAGE or the SDS-PAGE when the samples were not heat treated. Comparison of seven complete amino acid sequences from seven species of Haloarcula_and those from Har. californiae and Har. japonica, whose N-terminal 3 amino acids have not been determined yet, revealed that they are very similar and differed at only 1 to 4 residues in 153 residues. NDKs from Haloarcula quadrata and Har. sinaiiensis differed only at the 30th amino acid (arginine vs. cysteine), yet they showed a remarkable difference in their salt-response patterns, suggesting that a single amino acid substitution can cause a one molar shift in the optimal NaCl concentration.