PubMed · 4702463
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
J A O'Connell. 1973. Improving titration accuracy.. https://pubmed.ncbi.nlm.nih.gov/4702463/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The mass spectra of several compounds with molecular weights in the 2500-20,000 Da range were obtained with a quadrupole mass spectrometer equipped with an atmospheric pressure ion source. Average molecular weight determinations of mellitin (2846.4 Da), a synthetic oligonucleotide (4262.8 Da), myoglobin (16,950.4 Da) and on the subunits of beta-lactoglobulin (18,277.1 Da) requiring as little as 1 pmol of material were achieved with accuracies and precisions of +/- 1 Da. An ion-spray interface was used to produce ions via the ion evaporation process, producing mass spectra containing a series of multiply-charged molecular species. A simple method for calculating the molecular weight of unknown compounds from the spectra containing multiply-charged ions is described.
Results obtained from gel filtration showed that beta-lactoglobulin binds p-nitrophenyl phosphate with a stoichiometry of 1 mol of ligand per 18,360 monomer. Circular dichroic spectra confirmed the binding and implicated tryptophan and phenylalanine residues in the interaction. Fluorescence of the protein was quenched on binding also supporting complex formation; analysis of these data indicates that p-nitrophenyl phosphate binds to beta-lactoglobulin A with a dissociation constant of 31 microM. The B and C genetic variants of beta-lactoglobulin bind p-nitrophenyl phosphate with dissociation constants of 63 and 70 microM, respectively. In addition, a series of other nitrophenyl compounds and pyridoxal phosphate were also investigated by fluorescence analysis and found to bind to the protein. These results are discussed with respect to a recent hypothesis that beta-lactoglobulin binds retinol and is structurally related to serum retinol binding protein.
1. A theory based on a multiple equilibrium model with stoicheiometric binding constants has been formulated. It is applicable to the interaction of amphipathic molecules with charged macromolecules. 2. The theory has been applied to the binding of sodium n-dodecyl sulphate to ribonuclease A, beta-lactoglobulin and bovine serum albumin. 3. Over the ranges of surfactant concentration where binding is non-co-operative and co-operative, the experimental data can be satisfactorily fitted with energy and co-operatively parameters which are of comparable magnitude for the three globular proteins. 4. The results imply that the energy of interaction of sodium n-dodecyl sulphate with the proteins is equivalent to the formation of approximately four CH2 hydrophobic bonds.