A water-soluble yellow protein, previously discovered in the purple photosynthetic bacterium Ectothiorhodospira halophila, contains a chromophore which has an absorbance maximum at 446 nm. The protein is now shown to be photoactive. A pulse of 445-nm laser light caused the 446-nm peak to be partially bleached and red-shifted in a time less than 1 microsecond. The intermediate thus formed was subsequently further bleached in the dark in a biphasic process occurring in approximately 20 ms. Finally, the absorbance of native protein was restored in a first-order process occurring over several seconds. These kinetic processes are remarkably similar to those of sensory rhodopsin from Halobacterium, and to a lesser extent bacteriorhodopsin and halorhodopsin; although these proteins are membrane-bound, they have absorbance maxima at about 570 nm, and they cycle more rapidly. In attempts to remove the chromophore for identification, it was found that a variety of methods of denaturation of the protein caused transient or permanent conversion to a form which has an absorbance maximum near 340 nm. Thus, by analogy to the rhodopsins, the absorption at 446 nm in the native protein appears to result from a 106-nm red shift of the chromophore induced by the protein. Acid denaturation followed by extraction with organic solvents established that the chromophore could be removed from the protein. It is not identical with all-trans-retinal and remains to be identified, although it could still be a related pigment. The E. halophila yellow protein has a circular dichroism spectrum which indicates little alpha-helical secondary structure (19%).(ABSTRACT TRUNCATED AT 250 WORDS)

Sutlzmary 9-Chloro-cis4-cyclononatetraene undergoes rapid solvolytic rearrangement to exo-l-chloro-cis-8,9-dihydroindene, via the cyclononatetraenyl cation. THE cis4-cyclononatetraenyl cation(1) is an interesting 877 monocycle, since its dimensions are such as to allow planar as well as puckered geometries. Recently Schleyer, Boche, and their co-workers' presented evidence, based on rate data and deuterium labelling experiments, that thermolysis of anti-9-chlorobicyclo [6,1,0]nona-2,4,6-triene in aqueous acetone proceeds by what appears to be (1).We now report on the ready solvolytic generation of (1) from 9-chloro-cis4-cyclononatetraene (2a) .l 9-Chloro-cis4-cyclononatetraene (2a) rearranges cleanly and irreversibly to exo-l-chloro-cis-8,9-dihydroindene (3a) on mild heating in CDCl,, the conversion being characterized by t)(Oo) ca. 70min (AF: ca. 21 kcalmol-'). The same bond relocation (2a) -+ (3a)f also obtains in SO, although far more rapidly, e.g., t i ( -66') < 10 min, (AF* < 15 kcal mol-l).: The greatly enhanced rate of this conversion in the more ionizing medium (SO,) raised the question of whether rearrangement here might not be chiefly activated by initial ionization of (2). In order to test this possibility it was necessary to assess the thermal fate of appropriately labelled (2). We therefore prepared the monodeuterio-compound (2b) by exposing anti-9-chloro-7 Significantly, we find anti-9-chlorobicyclo[6,1,0]nona-2,4,6-triene to be inert in SO, a t -20".

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Horse heart cytochrome c can be split with cyanogen bromide into a heme peptide (residues 1-65) and a nonheme peptide (residues 66-104). In a process involving (i) complex formation between the two fragments and (ii) restoration of the severed peptide linkage, a fully active cytochrome c preparation can be re-formed. Use has been made of this process to couple the heme peptide to peptide 66-104 synthesized by the Merrifield solid-phase procedure. The semisynthetic product formed in this manner is indistinguishable from reconstituted cytochrome c prepared with nonsynthetic peptide 66-104.

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