Biomaterial Database

Gramicidin S synthetase. Temperature dependence and thermodynamic parameters of substrate amino acid activation reactions. 1985

J Vater, and N Mallow, and S Gerhardt, and A Gadow, and H Kleinkauf

In the biosynthesis of the cyclic decapeptide antibiotic gramicidin S, the constituent amino acids are activated by a two-step mechanism involving aminoacyl adenylate and thio ester formation which are both reversible processes. The dissociation constants (KD) for the gramicidin S synthetase-substrate amino acid-thio ester complexes are 100-1000-fold lower compared to the KM data of the preceding aminoacyl adenylate reactions. The affinity for these substrates is appreciably higher at the thio template sites than at the aminoacyl adenylate reaction centers. Therefore, the activation equilibria are quantitatively shifted toward thio ester formation. A set of thermodynamic parameters for the activation processes was determined from the temperature dependence of the KM and KD data. Reaction enthalpies were obtained from a van't Hoff analysis of these constants. delta G degree for the substrate activation reactions of the heavy enzyme of gramicidin S synthetase (GS 2) is predominantly controlled by entropy contributions. In contrast, the overall activation and concomitant racemization of phenylalanine by phenylalanine racemase (GS 1) are exothermic processes which are distinguished by a small negative reaction entropy.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D009097	Multienzyme Complexes	Systems of enzymes which function sequentially by catalyzing consecutive reactions linked by common metabolic intermediates. They may involve simply a transfer of water molecules or hydrogen atoms and may be associated with large supramolecular structures such as MITOCHONDRIA or RIBOSOMES.	Complexes, Multienzyme
D010453	Peptide Synthases	Ligases that catalyze the joining of adjacent AMINO ACIDS by the formation of carbon-nitrogen bonds between their carboxylic acid groups and amine groups.	Peptide Synthetases,Acid-Amino-Acid Ligases,Acid Amino Acid Ligases,Ligases, Acid-Amino-Acid,Synthases, Peptide,Synthetases, Peptide
D010761	Phosphorus Radioisotopes	Unstable isotopes of phosphorus that decay or disintegrate emitting radiation. P atoms with atomic weights 28-34 except 31 are radioactive phosphorus isotopes.	Radioisotopes, Phosphorus
D002250	Carbon Radioisotopes	Unstable isotopes of carbon that decay or disintegrate emitting radiation. C atoms with atomic weights 10, 11, and 14-16 are radioactive carbon isotopes.	Radioisotopes, Carbon
D000591	Amino Acid Isomerases	Enzymes that catalyze either the racemization or epimerization of chiral centers within amino acids or derivatives. EC 5.1.1.	Amino Acid Racemase,Amino Acid Racemases,Acid Isomerases, Amino,Acid Racemase, Amino,Acid Racemases, Amino,Isomerases, Amino Acid,Racemase, Amino Acid,Racemases, Amino Acid
D000596	Amino Acids	Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins.	Amino Acid,Acid, Amino,Acids, Amino
D001407	Bacillus	A genus of BACILLACEAE that are spore-forming, rod-shaped cells. Most species are saprophytic soil forms with only a few species being pathogenic.	Bacillus bacterium
D013379	Substrate Specificity	A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts.	Specificities, Substrate,Specificity, Substrate,Substrate Specificities
D013696	Temperature	The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.	Temperatures