title: N5,N10-methenyltetrahydromethanopterin cyclohydrolase from the extremely thermophilic sulfate reducing Archaeoglobus fulgidus: comparison of its properties with those of the cyclohydrolase from the extremely thermophilic Methanopyrus kandleri.
abstract: Archaeoglobus fulgidus and Methanopyrus kandleri are both extremely thermophilic Archaea with a growth temperature optimum at 83 degrees C and 98 degrees C, respectively. Both Archaea contain an active N5,N10-methenyltetrahydromethanopterin cyclohydrolase. The enzyme from M. kandleri has recently been characterized. We describe here the purification and properties of the enzyme from A. fulgidus. The cyclohydrolase from A. fulgidus was purified 180-fold to apparent homogeneity and its properties were compared with those recently published for the cyclohydrolase from M. kandleri. The two cytoplasmic enzymes were found to have very similar molecular and catalytic properties. They differed, however, significantly with respect of the effect of K2HPO4 and of other salts on the activity and the stability. The cyclohydrolase from A. fulgidus required relatively high concentrations of K2HPO4 (1 M) for optimal thermostability at 90 degrees C but did not require salts for activity. Vice versa, the enzyme from M. kandleri was dependent on high K2HPO4 concentrations (1.5 M) for optimal activity but not for thermostability. Thus the activity and structural stability of the two thermophilic enzymes depend in a completely different way on the concentration of inorganic salts. The molecular basis for these differences are discussed.
authors: Laboratorium für Mikrobiologie des Fachbereichs Biologie, Philipps-Universität, Marburg/Lahn, Germany.
authors: A R
authors: AR
authors: Klein
authors: J
authors: J
authors: Breitung
authors: D
authors: D
authors: Linder
authors: K O
authors: KO
authors: Stetter
authors: R K
authors: RK
authors: Thauer
mesh_terms: D000595:Amino Acid Sequence; D000619:Aminohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001105:Archaea / Q000201:enzymology* / Q000235:genetics; D004795:Enzyme Stability; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010802:Phylogeny; D012492:Salts; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013696:Temperature
chemical_list: D012492:Salts; D000619:Aminohydrolases; C050675:methenyltetrahydromethanopterin cyclohydrolase