Electrocatalytic properties of polypyrrole in amperometric electrodes

The electrocatalytic oxidation of NADH, ascorbate, urate, xanthine and H₂O₂ at different polypyrrole electrodes has been investigated. The conducting polymer was grown on platinum, glassy carbon, or graphite electrodes and modified by means of enclosed redox-active anions or other redox-active compounds covalently bound to either the N- or the β-position of the pyrrole. Copolymers of pyrrole and N-substituted pyrrole derivatives of chloranil or 2,3-dicholoro-1,4-naphthoquinone showed outstanding electrocatalytic properties for the oxidation of NADH. The application of these electrodes in amperometric steady-state measurements or flow-injection systems in combination with dehydrogenase reactions has been possible.     

Conformational study of native and acid-dissociated states of porcine lutropin (pLH) by vacuum circular dichroism and ultraviolet absorption spectroscopy

Porcine lutropin shares with ovine lutropin common structural features. They exhibit identical vacuum circular dichroism down to 170 nm with characteristic negative bands at 173, 194, and 210 nm. The band at 210 ± 1 nm is shifted to 201 nm upon dissociation with disappearance of the 194-nm band. For the two hormones the acid transition involves a significant loss of the three recognized periodic structures α helix, β sheet, and β turns of type II, unshields near the same number of tyrosyl residues (2.2 ± 0.7), and gives rise to an identical absorption difference at 287 nm in a two-step mechanism. However, pLH also exhibits noticeable differences: 5 to 10 times lower rates of acid transition with a lower pK_a (3.7 ± 0.1) and different transition behavior of tyrosine residues compared to ovine lutropin.     

Neurophysiology of the vibration sense in locusts and bushcrickets: Response characteristics of single receptor units

The response characteristics of the vibration receptors in the legs of the migratory locust, Locusta migratoria, and the tettigoniid Decticus verrucivorus were investigated electro-physiologically by single cell recordings. The legs were stimulated by sinusoidal vibrations. There are four types of vibration receptor in each leg of Locusta and Decticus, which can be classified physiologically. One type—most probably campaniform sensilla—shows a phase-locked response to vibrations from 30 to 200 Hz, its threshold reflecting the displacement. A second type shows similar responses in the same frequency range, but its reactions depend on the stimulus acceleration. The receptor cells of the subgenual organ are very sensitive to vibration from 30 to at least 5000 Hz, and their responses depend on acceleration. There are two types of subgenual receptors, one of which shows a clear maximum of sensitivity between 200 and 1000 Hz, with a threshold below 0.01 m/sec^?2 acceleration. Subgenual receptors with different thresholds and different characteristic frequencies occur in each leg. The receptors of each leg pair have quite similar mean sensitivities and characteristic frequencies. However, in the front legs of tettigoniids the more sensitive subgenual receptors and an additional receptor type also respond to low-frequency airborne sound up to 10 kHz.     

Predominance of gonadotropin α-subunit resulting from preferential loss of hCGβ production in an established cell line

Summary The BeWo line of trophoblastic cells, maintained in continuous culture since 1966, was employed to investigate the phenomenon of gonadotropin α-subunit predominance that exists in several cell lines. The secretion of complete human chorionic gonadotropin (hCG) relative to α-subunit was compared in several different BeWo sublines, all of which were derived from BeWo stock roller tube colonies. In all of the BeWo sublines, secretion of hCG originally exceeded secretion of α-subunit. With time in culture, however, there was a marked decline in production of hCG/hCGβ, but not in α-subunit. Thus it appears that the production of hCGβ by BeWo choriocarcinoma cells is more labile than the production of the α-subunit.     

The reaction of the mutagen 1,1′-hexamethylene-bis[(5-p-chlorophenyl)-biguanide] with guanosine and cysteine

The mutagen 1,1′-hexamethylene-bis[(5-p-chlorophenyl)-biguanide] reacts at 37°C with guanosine and guanine to yield xanthosine or xanthine and oxidizes cysteine to cystine. After treatment of a guanosine-labelled DNA sample from Escherichia coli with the mutagen xanthine could be detected as a reaction product. At a slow rate the mutagen is hydrolysed spontaneously yielding urea, 1,6-hexanediol and 4-chloroaniline. The reaction mechanisms both of the hydrolysis and of the reaction with cysteine and guanosine are discussed.     

Current-voltage studies on the thylakoid membrane in the presence of ionophores

The reversibility of the binding of ionophores to the thylakoid membrane is studied. While gramicidin binds practically irreversibly, valinomycin and nonactin bind reversibly, however, only a small fraction (about 1 %) of the membrane-bound valinomycin or nonactin is active in ion transport. The current-voltage relationship is evaluated under these circumstances. We have found that it is practically linear. This together with the relationship between current and ion concentration agrees qualitatively with the results reported for bimolecular lipid membranes, which contain a large fraction of negatively charged lipids. For the ionophores, valinomycin and nonactin, the binding equilibria (K ≈ 10⁴) and the turnover numbers (≈ 3 · 10⁴/s) are evaluated for their action on the thylakoid membrane. Possible reasons for the inactivity of the majority of membrane-bound ionophore molecules are discussed.