Organ cultures of individual rat pineals incorporate (14)C-tryptophan into proteins at a nearly constant rate for at least 48 hours. Previous studies have shown that these cultures also convert (14)C-tryptophan to serotonin, melatonin, and 5-hydroxyindoleacetic acid, and release these indoles into the media. The formation of (14)C-protein from (14)C-tryptophan is accelerated by the addition to ...

Every lipid membrane fission event involves the association of two apposing bilayers, mediated by proteins that can promote membrane curvature, fusion and fission. We tested the hypothesis that Fis1, a tail-anchored protein involved in mitochondrial and peroxisomal fission, promotes changes in membrane structure. We found that the cytosolic domain of Fis1 alone binds lipid vesicles, which is en...

In constant pH molecular dynamics simulations, the protonation states of titratable sites can respond to changes of the pH and of their electrostatic environment. Consequently, the number of protons bound to the biomolecule, and therefore the overall charge of the system, fluctuates during the simulation. To avoid artifacts associated with a non-neutral simulation system, we introduce an approa...

Protonation of key histidine residues has been long implicated in the acid-mediated cellular action diphtheria toxin translocation (T-) domain, responsible for delivery catalytic domain into cell. Here, we use a combination computational (constant-pH Molecular Dynamics simulations) and experimental (NMR, circular dichroism, fluorescence spectroscopy along with X-ray crystallography) approaches ...

The acid-base chemistry that drives catalysis in pyridoxal-5'-phosphate (PLP)-dependent enzymes has been the subject of intense interest and investigation since the initial identification of PLP's role as a coenzyme in this extensive class of enzymes. It was first proposed over 50 years ago that the initial step in the catalytic cycle is facilitated by a protonated Schiff base form of the holoe...

In Bacillus subtilis, expression of the tryptophan biosynthetic genes is regulated in response to tryptophan by an RNA-binding protein called TRAP (trp RNA-binding attenuation protein). TRAP has been shown to contain 11 identical subunits arranged in a symmetrical ring. Kinetic and thermodynamic parameters of the interaction between tryptophan-activated TRAP and trp leader RNA were studied. Res...

In this study, a potentiometric titration method for the determination of montelukast sodium in pharmaceutical dosage forms was developed and validated. For this purpose, the potentiometric titration of the standard montelukast sodium was carried out using hydrochloric acid as titrant. The method was found to be highly accurate and precise, having a relative standard deviation of less than 1.0%...

The kinetics of actin unfolding induced by guanidine hydrochloride has been studied. On the basis of obtained experimental data a new kinetic pathway of actin unfolding was proposed. We have shown that the transition from native to inactivated actin induced by guanidine hydrochloride (GdnHCl) passes through essential unfolding of the protein. This means that inactivated actin should be consider...

The fluorescence of tryptophan residues of gramicidin A (gA), bound to phosphatidylcholine liposomes contains valuable information about local changes in the environment of the molecule induced by gamma radiation. With this work, we aim to demonstrate that the gamma radiation effect on the peptide involves the action of free radicals, derived from water radiolysis and the process of lipid perox...

Because of their central importance for understanding enzymatic mechanisms, pK(a) values are of great interest in biochemical research. It is common practice to determine pK(a) values of amino acid residues in proteins from NMR or FTIR titration curves by determining the pH at which the protonation probability is 50%. The pH dependence of the free energy required to protonate this residue is th...