TERMIUM Plus®

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INTERMEDIATE FORMATION [2 records]

Record 1 2011-01-10

English

Subject field(s)
  • Biological Sciences
DEF

Catalysis where an electrophilic or nucleophilic group on the peptide chain of the enzyme forms a covalent bond with the substrate. This highly reactive covalent intermediate between the enzyme and the substrate has a high probability of entering the transition state permitting the substrate to find a lower pass over the activation-energy barrier.

CONT

Many of the examples of covalent catalysis in enzyme-catalysed reactions involve attack by a nucleophilic side chain at an electron-deficient centre in the substrate; such attack is termed nucleophilic catalysis. Examples of nucleophilic catalysis are provided by chymotrypsin and fructose-bisphosphate aldolase, in these cases the nucleophilic side chains are those of serine and lysine respectively. Other types of side chain which have been found to participate in nucleophilic catalysis include cysteine ... and histidine....

French

Domaine(s)
  • Sciences biologiques
CONT

La catalyse covalente est utilisée par certains enzymes pour augmenter la vitesse d'une réaction chimique, en formant un intermédiaire covalent hautement réactif entre l'enzyme et le substrat qui possède une grande probabilité d'entrer dans l'état transitoire; ceci permet au substrat de trouver un passage plus bas pour traverser la barrière d'énergie d'activation. La catalyse covalente est de règle dans les réactions auxquelles participent les coenzymes : ainsi, le pyridoxal-phosphate participe à la décarboxylation oxydative des acides aminés par l'intermédiaire d'une base de Schiff, aisément mise en évidence par son spectre optique caractéristique. La plupart des transferts de phosphyryls à partir de l'ATP exigent une phosphorylation intermédiaire de l'enzyme, en général sur un résidu histidine, etc.

Spanish

Save record 1

Record 2 2000-02-09

English

Subject field(s)
  • Geology

French

Domaine(s)
  • Géologie
OBS

[...] modérément consolidée.

Spanish

Save record 2

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