An electron nuclear double resonance investigation of redox-induced electronic structural change at CuA2+ in cytochrome c oxidase

We measured an electronic change at cysteine ligand(s) of the CuA2+ center brought on by reduction of other metal centers within cytochrome c oxidase, notably cytochrome a. This change specifically manifested itself as a modification in magnetic hyperfine coupling to the beta-protons of the beta-carbons adjacent to the cysteine sulfur in the CuA2+ coordination sphere. The electron nuclear double resonance ENDOR signals of these beta-protons had previously been assigned through study of selectively deuterated yeast oxidase. In the present study the ENDOR signals of the CuA2+ center were compared from the following forms of oxidase: resting (a3+.CuA2+.a3+3.CuB2+); mixed valence, 2-electron-reduced CO-ligated oxidase (a3+.CuA2+.a2+3CO.CuB+), and a more completely reduced mixed-valence CO-ligated oxidase. In agreement with previous studies on 3-electron-reduced oxidase, the latter more completely reduced oxidase showed cytochrome a preferentially reduced with respect to CuA, implying that the majority of paramagnetic CuA2+ centers had reduced cytochrome a partners. The ENDOR-resolved splitting of the beta-proton hyperfine features substantially decreased in going from the first two more oxidized forms to the more fully reduced latter form. Thus, the electronic structure of the CuA2+ center specifically monitored by hyperfine couplings to cysteine protons changed in response to a reductive event elsewhere in the protein. This structural change may correlate with the anticooperative redox interaction recently reported between cytochrome a and CuA.     

Transdermal delivery of a melanotropic peptide hormone analogue

We previously reported that topical application of [Nle4,D-Phe7]alpha-MSH, a superpotent analogue of alpha-melanocyte stimulating hormone, to mice induces a darkening of follicular melanocytes throughout the skin. We now report that the melanotropin analogue can be delivered across mouse but not rat skin in an in vitro model system. Passage of the analogue from the topically applied vehicle (polyethylene glycol) across the skin into a subcutaneous receiving vessel was demonstrated by both bioassay as well as by radioimmunoassay. The bioassay data demonstrate that percutaneous absorption of the melanotropin did not result in loss of biological activity of the peptide. The differential penetration of the peptide across rodent skin reveals that one cannot predict percutaneous absorption of a substance across the stratum corneum from studies on a single species. The present results are the first to demonstrate, by direct quantitative measurements, that a bioactive peptide can be delivered across the vertebrate integument in vitro. These studies point out the potential of a topically applied melanotropin for tanning of the skin and possibly for treatment of certain hypopigmentary disorders.     

Protein labeling by reductive methylation with sodium cyanoborohydride: Effect of cyanide and metal ions on the reaction

Previous studies (N. Jentoft and D. G. Dearborn, 1979, J. Biol. Chem.254, 4359) have demonstrated that reductive methylation with labeled formaldehyde and NaCNBH₃ provides a simple method for specifically labeling the amino groups of proteins using extremely mild reaction conditions. However, cyanide, which is one of the products of the reaction, reduces labeling effciency by reacting with formaldehyde to from the formaldehyde cyanohydrin addition product. Certain transition metal ions are able to prevent this secondary reaction by forming stable coordination complexes with cyanide. Inclusion of millimolar quantities of Ni(II) in reaction mixtures leads to a 20–30% increase in protein labeling so that maximal derivatization of amino groups can be realized with only a 3- to 4-fold ratio of formaldehyde to amine rather than the 5- to 10-fold excess necessary in the absence of metal ions.     

Ayenia saligna (Sterculiaceae), a new species from Colombia

Ayenia saligna from Colombia is described and illustrated. It is remarkable for having foliar nectaries, which now are known to occur in seven of the 75–80 species in the genus. The petals ofAyenia are structurally complex and the inconsistent use of terminology to describe their parts is noted. In addition, the relationship ofA. saligna to other species ofAyenia is discussed.     

A striking,new species of Roupala (Proteaceae) from the Venezuelan Andes

Roupala barnettiae from the Montañas de Misisí in Edo. Trujillo, Venezuela is described and illustrated. Its taxonomic affinities are also discussed.