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Two photochromic activators of the electrogenic membrane of the electroplax of Electrophorus electricus are described. monium)methyljazobenzene dibromide (Bis-Q), one of the most potent ever reported, is active at concentrations of less than 10-7 M. Its cis isomer, which is obtained from the trans by exposure to light of 330 nm, is practically devoid of activity. Photoregulation of the potential of the membrane takes place in the presence of Bis-Q, presumably because of the conversion of the active trans isomer to the inactive cis isomer in the single-cell electroplax system.The second activator, 3-(a-bromomethyl)-3'-[a-(trimethylammonium)methyllazobenzene bromide (QBr) can be covalently attached to the electroplax membrane after reduction of the membrane with dithiothreitol. Activation of the membrane is induced by the covalently linked reagent. Its cis isomer, obtained from the trans by exposure to light of 330 nm, is, like cis-Bis-Q, of very low activity. Both isomers of Bis-Q are equally active as inhibitors of acetylcholinesterase, 50% inhibition occurring at a concentration of 10-5 M. The possibility of using trans-Bis-Q and trans-QBr to characterize and isolate the receptor protein is discussed.Systems in which photoregulation could be studied at the molecular level were described in previous papers. In these systems, photochromic azo derivatives were used as effector molecules to regulate the activities of chymotrypsin (1) and acetylcholinesterase (2, 3) and to photoregulate the potential of the excitable membrane of the monocellular electroplax preparation (4). Photoregulation was achieved by exploiting differences between the biochemical activities of the cis and trans isomers of the photochromic compounds, the relative concentrations of which were influenced by the wavelength of light to which the solution was exposed [or light vs. darkness, in one case (3) ].Light-induced changes in potential of the electroplax membrane may be considered as a Mtodel for the process of vision, in which the cis to trans isomerization of retinal is the first step in the initiation of a neural impulse. In the latter case, however, as well as in the phytochrome system of plants (5), the photochromic substances are located intracellularly, making for a highly efficient process. It thus appeared of interest to prepare a light-sensitive ligand that would form a covalent bond with the receptor protein of the electroplax. A compound with the desired properties was prepared: 3-(a-bromomethyl)-3'-[a-(trimethylammonium)methyl]azobenzene (QBr). Also synthesized was the closely related 3,3'-bis[a-(trimethylammonium)methyl]azobenzene (Bis-Q). the trans isomer of which was found to be a potent receptor activator, one of the most potent thus far described.The high affinity and specificity of Bis-Q may make it a useful reagent for the characterization, isolation, and purification of the receptor protein. Some experiments with the two azo compounds are presented in this paper. METHODSPreparation of 3,3'-bis(a-bromomethyl)azobenz...

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c or reduced phenazine methosulfate coupled with the reduction of ubiquinone. We wish to report now that chromatophores from aerobically grown R. spheroides, strain Ga, sensitize these reactions efficiently (with quantum requirements of a few quanta per electron transfer), whereas chromatophores from the nonphotosynthetic mutant strain PM-8 are entirely unable to drive these photochemical processes. The failure of strain PM-8 to catalyze the photooxidation of reduced phenazine methosulfate is the more remarkable because this reaction is sensitized by purified bacteriochlorophyll in vitro. These findings show that the major component of bacteriochlorophyll is inert with respect to the foregoing light-induced activities, and that a special kind of reaction center is needed for the photochemistry that leads to photosynthesis. The results of experiments with exogenous reagents will be published in detail elsewhere. We are indebted to Dr. W. S. Zaugg for making available both the chemicals and the methodology for studying the photochemical electron transfer reactions of cytochrome, phenazine methosulfate, and ubiquinone. * Contribution no. 157 from the Charles F. Kettering Research Laboratory.

The recent interest in using Buckminsterfullerene (fullerene) derivatives in biological systems raises the possibility of their assay by immunological procedures. This, in turn, leads to the question of the ability of these unprecedented polygonal structures, made up solely of carbon atoms, to induce the production of specific antibodies. Immunization of mice with a C 60 fullerene derivative conjugated to bovine thyroglobulin yielded a population of fullerene-specific antibodies of the IgG isotype, showing that the immune repertoire was diverse enough to recognize and process fullerenes as protein conjugates. The population of antibodies included a subpopulation that crossreacted with a C 70 fullerene as determined by immune precipitation and ELISA procedures. These assays were made possible by the synthesis of water-soluble fullerene derivatives, including bovine and rabbit serum albumin conjugates and derivatives of trilysine and pentalysine, all of which were characterized as to the extent of substitution and their UV-Vis spectra. Possible interactions of fullerenes with the combining sites of IgG are discussed based on the physical chemistry of fullerenes and previously described protein-fullerene interactions. They remain to be confirmed by the isolation of mAbs for x-ray crystallographic studies.

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