Model for the porphyrin-DNA binding site: ENDOR investigations of Cu-porphyrins binding to DNA.

Proton ENDOR has been observed from frozen solutions (ca. 38K degrees) of copper meso-(4-N-tetra-methylpyridyl)porphyrin (CuTMpyP(4)) complexed with Salmon sperm DNA in water and D2O. Lines from exchangeable protons of the DNA bases have been observed in these ENDOR spectra. Analyses of these ENDOR data show that the separations of these DNA protons from the copper atom are between 3.76 and 3.84 A with angles of 19.5 to 22.5 degrees between the Cu-H vectors and the gz axis. A distant ENDOR response has also been observed from phosphorous nuclei in the DNA backbone. We estimate that the phosphorous atoms producing this ENDOR signal are 7.5-10 A from the copper center of the porphyrin. These ENDOR data combined with results from an earlier NMR investigation have been used to construct a computer simulated model of the binding site in which the porphyrin is partially intercalated and extends into the major groove of DNA. The two GC base pairs at this site are slightly inequivalent. For each, the G imino proton and one of the C amino protons are at appropriate positions to account for the ENDOR signals arising from exchangeable protons. It is unlikely that this inequivalence would persist at room temperature where dynamic processes would give an apparently symmetric interaction. Although the model accounts for all reported experimental data involving tetracationic porphyrin species which have been suggested to be intercalators, it is not a unique solution.

Nicotine-induced membrane perturbation of intact human granulocytes spin-labeled with 5-doxylstearic acid. Correlation with chemotaxis.

The effects of nicotine on intact human granulocytes were examined, using 5-doxylstearic acid as a spin probe. At micromolar concentrations, (-)-nitocine produces a membrane perturbation in granulocytes not observable with oriented lipid bilayers. The effect, which is stereoselective for the (-)-isomer, occurs at concentrations of nicotine that bind to noncholinergic nicotine receptors on granulocytes and which are present in the blood after smoking. At comparable concentrations, (-)-nicotine modulates granulocyte chemotaxis towards a chemotactic peptide in a stereospecific and dose-dependent manner. Cotinine, the major metabolite of nicotine, does not bind to the receptor, does not produce the membrane perturbation observed with nicotine, and has no effect on chemotaxis. These results suggest that (-)-nicotine present in the blood after smoking binds to a receptor on granulocytes, perturbs granulocyte membranes and modulates chemotaxis.

Affinity labeling and purification of the opiate receptor from rat brain.

Affinity labeling of the opiate receptor has been performed on neural membranes from rat brain utilizing[125I]-14-bromoacetamidomorphine, an opiate agonist, and [125I]-14-chloracetylmorphine, an antagonist. With the use of SDS gel electrophoresis it could be shown that the agonist labeled three proteins with molecular weights of 43,000, 35,000 and 23,000, whereas the antagonist only labeled the 23,000 component. The preferential labeling of the 23,000 protein by the antagonist suggests that this component may be a primary recognition site for opiate antagonists. Calcium was stimulatory to the affinity labeling of all three proteins while sodium was inhibitory. With the use of affinity columns prepared by conjugating either ligand to omega-aminohexyl Sepharose, a receptor complex was obtained consisting all three proteins. Stereospecific opiate binding was demonstrable in the complex prepared from either column.