Biomedical subjects

W W Mantulin

Publications and source records attributed to W W Mantulin.

26 records · Page 2Linked to original sources

PubMed1981

Reassembled model lipoproteins. Lipid dynamics in recombinants of human apolipoprotein A-II and dimyristoylphosphatidylcholine.

Dimyristoylphosphatidylcholine (DMPC) and apolipoprotein A-II (apoA-II) combine to form three isolatable complexes of molar stoichiometry of 240:1 75:1, and 45:1, respectively. Steady state fluorescence depolarization studies with diphenylhexatriene (DPH) and parinaric acid incorporated into the DMPC/apoA-II complexes reveal that increasing the protein content reduces fluidity and increases the apparent lipid phase transition (Tc). Time-resolved studies with DPH reveal hindered rotational motion and a loss of fluidity with increasing protein content, arising from an increase in the order of the lipid assay. The parinaric acid probes could detect no lateral phase separation of lipid ensembles in the DMPC/apoA-II complexes, suggesting that the DMPC adjacent to the protein is as mobile as bulk lipid. Measurements of the excimer-forming properties of a pyrene lecithin analog show that the increasing protein content in the DMPC/apoA-II complexes reduces lateral diffusion of the lipid.

Apolipoprotein A-II↗

PubMed1981

Low density lipoproteins reconstituted with steroids containing the nitrobenzoxadiazole fluorophore.

A new cholesterol analog, N-(7-nitrobenz-2-oxa-1,3-diazole)-23,24-dinor-5-cholen-22-amine-3 beta-ol, with fluorescent properties similar to those of fluorescein, has been synthesized. The fluorescence lifetimes, quantum yields, and wavelength maxima of N-(7-nitrobenz-2-oxa-1,3-diazole)-23,24-dinor-5-cholen-22-amine-3 beta-ol and its linoleate ester were solvent-dependent. The cholesterol analog was a satisfactory substrate for lecithin:cholesterol acyltransferase. The fluorescent sterol, added in ethanol, gave half-maximal suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in cultured human fibroblasts at 2.5 microM and was twice as effective as cholesterol. The fluorescent steryl ester, incorporated into low density lipoprotein, was used to demonstrate high affinity cellular uptake and degradation of the reconstituted lipoproteins, intracellular accumulation of the free sterol and simultaneous suppression of 3-hydroxy-3-methylglutaryl coenzyme a reductase in fibroblasts. Half-maximal suppression was achieved at 10 micrograms mL-1 of low density lipoproteins reconstituted with the fluorescent steryl ester, compared to the same degree of suppression produced by 2 micrograms mL-1 of native low density lipoproteins. The interaction of low density lipoproteins reconstituted with N-(7-nitrobenz-2-oxa-1,3-diazole)-23,24-dinor-5-cholen-22-amine-3 beta-ol linoleate with cells was readily visualized by fluorescence microscopy and quantified by fluorimetry. These analogs will facilitate the studies of lipoprotein-cell interactions and phospholipid vesicle-cell interactions, the selection of cell mutants defective in lipoprotein metabolism, and the assessment of the immediate environment of the steroids in cellular membranes.

4-Chloro-7-nitrobenzofurazan↗

PubMed1980

The conformational properties of human plasma apolipoprotein C-II. A spectroscopic study.

The solution properties of human plasma apolipoprotein C-II (apoC-II) have been studied by analytical ultracentrifugation, circular dichroic spectroscopy, and fluorescence spectroscopy. ApoC-II self-associates in solution, even though no rigorous thermodynamic analysis of the mode of self-association could be established. The reversible denaturation of apoC-II by guanidinium chloride (GdmCl) proceeded in a sequential fashion. Initial disruption of protein self-association by 0.3 M GdmCl was followed by cooperative unfolding of monomeric protein at higher GdmCl concentratioans with a midpoint 1.1 M GdmCl. Based on tryptophan fluorescence quenching unfolded apoC-II was more permeable to penetration by small molecules than the self-associated protein. a very low free energy (delta GH2O = 2.8 kcal/mol) of denaturation was calculated from the GdmCl denaturation titration curve. Heating of apoC-II to 55 degrees C did not induce a reversible cooperative unfolding of the protein. Calculations, bsed on Chou-Fasman probability algorithms, reveal three sequential helical regions in apoC-II and one beta sheet structure (residues 61-74P. The locations of these regions are consistent with the known physiological functions of apoC-II.

Amino Acid Sequence↗

PubMed1977