Analysis of the experimental titration curves shows that gelatin contains acid groups with dissociation indices at pH 2.9 to 3.5 corresponding quantitatively with the content in dicarboxylic amino acids; and that the acidic group at pH 9.4 in egg albumin agrees with the amount of tyrosine. The amounts of histidine and lysine present in both these proteins agree quantitatively with basic groups ...

Here, we report the hypoxia-responsive ionizable liposomes to deliver small interference RNA (siRNA) anticancer drugs, which can selectively enhance cellular uptake of the siRNA under hypoxic and low-pH conditions to cure glioma. For this purpose, malate dehydrogenase lipid molecules were synthesized, which contain nitroimidazole groups that impart hypoxia sensitivity and specificity as hydroph...

The observation that 6 M-urea denatures horse ferricytochrome c in the pH range 4-6, but not horse ferrocytochrome c, has been exploited to determine the denaturation-induced proton uptake of ferricytochrome c. This is related to the pKa values of ionizable groups buried within the native protein. The data indicate that one of the haem propionic acid substituents of ferricytochrome c has a pKa ...

The toxicity of ionizable organic compounds to organisms depends on the pH, which therefore affects risk assessments of these compounds. However, there is not a direct chemical method to predict the toxicity of ionizable organic compounds. To determine whether hollow-fiber liquid-phase microextraction (HF-LPME) is applicable for this purpose, a three-phase HF-LPME was used to measure sulfadiazi...

We have investigated the binding of the serine protease inhibitor, turkey ovomucoid third domain (OMTKY3), to the serine protease, porcine pancreatic elastase (PPE), using isothermal titration calorimetry and structural energetics calculations. The calculations predict that the binding at 25 8C is characterized by a negligible DH 8, a large and positive DS 8, and a large and negative DCp, resul...

Protein-protein interactions depend on a host of environmental factors. Local pH conditions influence the interactions through the protonation states of the ionizable residues that can change upon binding. In this work, we present a pH-sensitive docking approach, pHDock, that can sample side-chain protonation states of five ionizable residues (Asp, Glu, His, Tyr, Lys) on-the-fly during the dock...

Voltage-gated sodium (Na+) channels are targets for local anesthetic (LA) drugs that bind in the inner pore of the channel with affinities related to the channel gating states. Our core model of the sodium channel (P loops and S5 and S6 segments from each of the four domains) was closed because it was developed using coordinates from the KcsA channel crystallographic structure. We developed a m...

The topography of lactose permease, in native membrane vesicles and after reconstitution of the purified protein into proteoliposomes, has been investigated by labeling the membrane-embedded portions of the protein using photoactivatable, hydrophobic reagents and by labeling the exposed portions of the protein with water-soluble, electrophilic reagents. Some sites of modification have been loca...

A hybrid quantum mechanics (QM)/molecular dynamics (MD) simulation is performed to investigate the effect of an ionizable group (-SO₃(-)Na⁺) on polyaniline as gas sensing materials. Polymers considered for this work include emeraldine base of polyaniline (EB-PANI) and its derivatives (Na-SPANI (I), (II) and (III)) whose rings are partly monosubstituted by -SO₃(-)Na⁺. The hybrid simulation resul...

The binding of nucleoside triphosphates to rabbit muscle phosphofructokinase has been determined in 0.05 M phosphate buffers by changes in intrinsic protein fluorescence and by direct binding measurements. These experiments have been performed over a wide range of pH, temperature, and effector concentration. Quenching of protein fluorescence is shown to measure binding of nucleotides to a site ...