Catalytic properties of thermophilic lactate dehydrogenase and halophilic malate dehydrogenase at high temperature and low water activity.
Eur J Biochem
; 183(1): 69-74, 1989 Jul 15.
Article
em En
| MEDLINE
| ID: mdl-2753046
ABSTRACT
Thermophilic lactate dehydrogenases from Thermotoga maritima and Bacillus stearothermophilus are stable up to temperature limits close to the optimum growth temperature of their parent organisms. Their catalytic properties are anomalous in that Km shows a drastic increase with increasing temperature. At low temperatures, the effect levels off. Extreme halophilic malate dehydrogenase from Halobacterium marismortui exhibits a similar anomaly. Increasing salt concentration (NaCl) leads to an optimum curve for Km, oxaloacctate while Km, NADH remains constant. Previous claims that the activity of halophilic malate dehydrogenase shows a maximum at 1.25 M NaCl are caused by limiting substrate concentration; at substrate saturation, specific activity of halophilic malate dehydrogenase reaches a constant value at ionic strengths I greater than or equal to 1 M. Non-halophilic (mitochondrial) malate dehydrogenase shows Km characteristics similar to those observed for the halophilic enzyme. The drastic decrease in specific activity of the mitochondrial enzyme at elevated salt concentrations is caused by the salt-induced increase in rigidity of the enzyme, rather than gross structural changes.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Bactérias Anaeróbias Gram-Negativas
/
Halobacterium
/
L-Lactato Desidrogenase
/
Malato Desidrogenase
Idioma:
En
Revista:
Eur J Biochem
Ano de publicação:
1989
Tipo de documento:
Article