The nucleotide sequences of the gene (pgk) encoding 3-phosphoglycerate kinase (PGK) from the mesophilic archaebacterium, Methanobacterium bryantii, and from the closely related thermophile, Methanothermus fervidus, were determined. The deduced amino acid (aa) sequences show 61% identity with each other and 32-36% identity with the enzyme homologues from eubacteria and eukaryotes. As found for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and l-malate dehydrogenase, the relatedness between the archaebacterial aa sequences on the one hand and the eubacterial or eukaryotic sequences on the other is lower than that between the latter ones. Comparison of the aa sequence of PGK from mesophilic and thermophilic archaebacteria indicates an increase of the overall hydrophobicity and a decrease of the chain flexibility in the thermophilic enzyme, as already deduced from respective comparison between GAPDH aa sequences of the same organisms. In addition, glycine residues are strikingly discriminated in the thermophilic PGK, which was also observed for GAPDH. Contrary to GAPDH, however, Lys and Arg residues are preferred in the thermophilic PGK. Lys to Arg substitutions are the most frequent cold-to-hot changes in PGK, whereas in GAPDH from the same organisms these changes do not occur. © 1990.
