Optimum pH For Stability Research Articles

Solution Stability of Factor Xa Inhibitors as a Function of pH

The stability of two factor Xa inhibitors (MLN1021 and CT54004) as a function of pH was investigated in order to better characterize the compounds and to locate the optimum pH for a stable formulation that might be used in a first‐in‐person (FIP) clinical study. The compounds prepared in buffer solutions over a pH range of 1–10 were stored at 60°C, and assayed for pH and purity at different time points. The pH‐rate profiles indicated that both compound was quite stable in the middle pH range, and least stable at pH < 3 and > 8. The optimum pH for stability of the compounds was around 6, which is consistent with the theoretical predictions by a mathematical model. The mechanism of the reaction is not a specific‐acid/base‐catalyzed reaction. Based on the experience of this study, an ideal experimental design is proposed, which will be useful for future study on similar drug candidate.

The influence of buffering on the stability of erythromycin injection in small-volume infusions

The influence of pH on the stability of erythromycin in small volume infusions indicated that the optimum pH for stability was greater than pH 7.5. Infusions containing erythromycin lactobionate injection buffered to pH 7.5–8.0 using sodium bicarbonate 8.4% were stable for 60 days, while unbuffered infusions containing similar quantities of the drug were stable for up to 20 days, based on t/95% calculations.

Purification and partial characterization of β-glucosidase from grape

β-Glucosidase was isolated from mature grapes (cv Muscat of Alexandria) and partially purified. The procedure used chromatography on Ultrogel AcA 44 and DEAE-Sepharose CL-6B. Two distinct peaks with β-glucosidase activity were reported. Except for their M r (98 000 for β-glucosidase 1, 50 000 for β-glucosidase 2) no differences occurred in other biochemical characteristics. For both, the optimum pH of activity was 5.0, the optimum pH for stability between 6 and 8, and the optimum temperature 45°. Their heat stabilities were also quite similar. The K m and V max values differ according the substrates. Affinity was maximal for p-nitrophenyl-β- d-glucoside. For natural substrates, the two enzymes had a high affinity for geranyl-β- d-glucoside. Glucose and gluconolactone were competitive inhibitors with K i of 170 and 0.215 mM respectively. Ca 2+ and Cu 2+ ions and p-chloromercuribenzoate also inhibited the enzymes.

Purification and characterization of endo‐xylanases from Aspergillus niger. II. An enzyme of pl 4.5

A homogeneous endo-xylanase (1,4-beta-D-xylan xylanohydrolase, EC 3.2.1.8) was obtained from a crude Aspergillus niger pentosanase by chromatography with Ultrogel AcA 54, SP-Sephadex C-25 at pH 4.5, DEAE-Sephadex A-25 at pH 5.4, Sephadex G-50, and SP-Sephadex C-25 with a gradient from pH 2.8 to pH 4.6. It was much more active on soluble than on insoluble xylan, yielding large amounts of unreacted xylan and a mixture of oligosaccharides with chain lengths from two to six. No xylose or L-arabinose was produced. There was high activity on a xylopentaose through xylononaose mixture, but not on xylobiose, xylotriose, or xylotetraose. The enzyme had slight activity on untreated cellulose, carboxymethylcellulose, and pectin. Molecular weight was ca. 1.4 x 10(4), with an isoelectric point of 4.5 and an amino acid profile high in acidic but low in sulfur-containing residues. In a 25-min assay at pH 4.7, this endo-xylanase was most active at 45 degrees C, with an activation energy from 5 to 35 degrees C of 33.3 kJ/mol. The optimum pH for activity was 4.9. Decay in buffer was first order, with an activation energy at pH 4.7 from 48 to 53 degrees C of 460 kJ/mol. Optimum pH for stability was about 5.6, where the half-life at 48 degrees C in buffer was ca. 40 h.

Purification and properties of glucose-6-phosphate dehydrogenase from Bacillus subtilis spores.

Glucose-6-phosphate dehydrogenase [D-glucose-6-phosphate: NADP oxidoreductase, EC. 1. 1. 1. 49] obtained from spores of Bacillus subtilis PCI 219 strain was partially purified by filtration on Sephadex G-200, ammonium sulfate fractionation and chromatography on DEAE-Sephadex A-25 (about 54-fold). The optimum pH for stability of this enzyme was about 6.3 and the optimum pH for the reaction about 8.3. The apparent Km values of the enzyme were 5.7 X 10(-4) M for glucose-6-phosphate and 2.4 X 10(-4) M for nicotinamide adenine dinucleotide phosphate (NADP). The isoelectric point was about pH 3.9. The enzyme activity was unaffected by the addition of Mg++ or Ca++. The inactive glucose-6-phosphate dehydrogenase obtained from the spores heated at 85 C for 30 min was not reactivated by the addition of ethylenediaminetetraacetic acid, dipicolinic acid or some salts unlike inactive glucose dehydrogenase.

Bacteriolytic enzymes from Staphylococcus aureus. Properties of the endo-beta-N-acetylglucosaminidase.

An extracellular bacteriolytic endo-beta-N-acetylglucosaminidase has been purified and its specificity of action has been investigated (Wadström & Hisatsune, 1970a,b). Some enzymic properties, such as optimum pH for enzyme activity on whole cells and cell walls of Micrococcus lysodeikticus and Staphylococcus aureus and optimum pH for stability, have been studied. The activity was maximum in 0.05m-tris-hydrochloric acid buffer, pH7.0. A higher ionic strength inhibited cell-wall hydrolysis. Since the crude and purified enzymes were found to be unstable on storage, the stabilizing and inhibiting effects of several compounds were investigated. Several heavy metal ions inactivated the enzyme at very low concentrations. Thiol compounds stabilized and thiol-reacting compounds partly inhibited the activity. Crude and purified glucosaminidase was found to be heat-stable at acidic pH and unstable at alkaline pH as previously found for several lysozymes (endo-beta-N-acetylmuramidases). Other properties of the staphylococcal enzyme and hen's-egg-white lysozyme have been compared, since the modes of action of the two are quite similar (Wadström & Hisatsune, 1970b).