Adenosine 5 -triphosphate mechanism

Pig. 2. Proposed mechanism of inbition of smooth muscle contraction by P2" gonists, where AMP is adenosine monophosphate, cAMP is cycHc-3 5 adenosine monophosphate, ATP is adenosine triphosphate, and -P is an attached phosphate. 

In the presence of calcium, the primary contractile protein, myosin, is phosphorylated by the myosin light-chain kinase initiating the subsequent actin-activation of the myosin adenosine triphosphate activity and resulting in muscle contraction. Removal of calcium inactivates the kinase and allows the myosin light chain to dephosphorylate myosin which results in muscle relaxation. Therefore the general biochemical mechanism for the muscle contractile process is dependent on the avaUabUity of a sufficient intraceUular calcium concentration. 

Lymn, R.W. Taylor, E.W. Mechanism of adenosine triphosphate hydrolysis of actomyosin. Biochemistry 10 4617-4624, 1971. 

Two examples where actin polymerization is observed in eukaryotes are in the bacterial pathogens Listeria monocytogenes and Shigella flexneri. The motion that the eukaryote pathogens exhibit is the actin based motility in the cytoplasm of their host. Actin polymerization is known to occur via an insertion polymerization mechanism. The movement is a result of site-directed tread-milling of the actin filaments. This type of movement is classified as a propulsive type motion. The driving force for actin pol)unerization as well as the next motor is the conversion of adenosine triphosphate (ATP) to adenosine diphosphate (ADP). ... 

For most amino acids, the ester linkage between the ct-COOH group of the amino acid and the 3 -terminal adenosine of a cognate tRNA is formed in a two-step mechanism catalyzed by an aminoacyl-tRNA synthetase (aaRS). ° In this so-called direct pathway, the aaRS first catalyzes the reaction of the amino acid with adenosine triphosphate (ATP), yielding the enzyme-bound high-energy intermediate aa AMP and PPi in the second step, this aaRS-bound intermediate reacts with tRNA to yield aa-tRNA and AMP (Figure 1). 

Mechanical Work. All cells exhibit motile and contractile properties. The remarkable thing about these activities of cells is that they are based on the direct coupling of chemical to mechanical action, in contrast to the heat engines that we have developed to perform our work for us. The mechanisms by which this coupling of chemical to mechanical processes takes place is not well understood, but the hydrolysis of adenosine triphosphate is known to be an important part of the molecular pathway. Although thermodynamic studies cannot provide information about the molecular steps involved, any mechanism that is proposed must be consistent with thermodynamic data [4]. 

Mechanism of Action A systemic anti-infective that inhibits the mitochondrial electron-transport system at the cytochrome bcl complex (Complex 111), which interrupts nucleic acid and adenosine triphosphate synthesis. Therapeutic Effect Antiprotozoal and antipneumocystic activity. 

Mechanism of Action Aproton pump inhibitor that is converted to active metabolites that irreversibly bind to and inhibit hydrogen-potassium adenosine triphosphates, an enzyme on the surface of gastricparietal cells. Inhibits hydrogen ion transport into gastric lumen. Therapeutic Effect Increases gastricpH, reducing gastric acid production. 

Uhr, M.L. Marcus, F. Morrison, J.F. Studies on adenosine triphosphate arginine phosphotransferase. Purification and reaction mechanism. J. Biol. Chem., 241, 5428-5435 (1966)... 

---