Absorption spectral properties of acetylated bacteriorhodopsin in purple membrane depending on pH

The dark-adapted form of bacteriorhodopsin in the purple membrane of Halobacterium halobium changes its absorption maximum from 560 to 600 nm if the pH is lowered to about 2 [Oesterhelt, D., & Stoeckenius, W. (1971) Nature (London), New Biol. 233, 149; Moore, T. A., Edgerton, M. E., Parr, G., Greenwood, C., & Perham, R. N. (1978) Biochem. J. 171, 469; Mowery, P. C., Lozier, R. H., Chae, Q., Tseng, T.-W., Taylor, M., & Stoeckenius, W. (1979) Biochemistry 18, 4100; Fischer, U., & Oesterhelt, D. (1979) Biophys. J. 28, 211; Muccio, D. D., & Cassim, J. Y. (1979) J. Mol. Biol. 135, 595]. We compared the pH dependence of the absorption spectra of acetylated membrane with that of unacetylated native membrane. The completely acetylated membrane showed a midpoint of pH 4.8 for the conversion to the acidic form; that of the native membrane was 3.4. On acetylation, the absorption maximum at neutral pH moved from 560 to 555 nm with about 20% decreases in extinction coefficients as compared with that of the native membrane, whereas the spectrum in acid was not affected. The chloride-dependent blue shift from the acidic form of the acetylated membrane was largely suppressed. The CD spectrum of the acetylated membrane was composed of two bands of an opposite sign with slightly decreased amplitudes. The chromophore of the acetylated membrane was sensitive to hydroxylamine, and the spectrum before bleaching was restored on addition of all-trans-retinal to the bleached membrane followed by dark incubation. Blue light irradiation accelerated the conversion to the acidic form in the native membrane but not in the acetylated membrane. Reductive ethylation did not affect the pH dependence of the absorption spectra.

Transverse myelitis associated with Mycoplasma pneumoniae infections

43-year-old man developed transverse myelitis following an infection with Mycoplasma pneumoniae. Among the uncommon neurological complications following infection with this organism, transverse myelitis has been reported rarely but may be more frequent than previously thought. Posterior spinal column involvement might result in a permanent neurological deficit despite the usually good prognosis.

Light-induced reaction of halorhodopsin prepared under low salt conditions

1. Membrane fraction containing halorhodopsin was prepared from the lysate of a mutant strain of Halobacterium halobium, Y1, which is defective in bacteriorhodopsin synthesis. 2. Irradiation of the membrane with red light at 0 degrees C decreased the absorbance intensities over the whole range of 500--600 nm and a new absorption peak appeared at about 400 nm. This process was reversed either by irradiation with blue light or simply by incubation in the dark. The wavelength at which the red light-induced absorbance decrease became maximum was 566 nm in the absence of NaCl and moved to 576 nm upon addition of NaCl. The midpoint for the conversion was at about 0.1 M NaCl. 3. Even though the membrane containing halorhodopsin was prepared in the absence of NaCl, this pigment was photochemically active in the sense that it could form a bathochromic photoproduct, a batho-intermediate, at -196 degrees C. 4. Retinal isomer composition during irradiation with red light at 0 degrees C was determined. Unirradiated halorhodopsin had predominantly all-trans retinal. With the increase of the blue-shifted product on irradiation, 13-cis content increased.

[Computed tomography in hypertensive cerebellar hemorrhage (author's transl)]

Fourteen cases of cerebellar hemorrhage were analysed from the point of CT-scan, and the following results were obtained. 1. The number of cases of cerebellar hemorrhage forms 4.4% of that of total intracranial hemorrhage. 2. Most of the cerebellar hematomas extend upward. Downward extension is rare. 3. In acute dead cases hematomas are 5 cm or more in diameter and lie over bilateral hemistpheres with the extension to third or fourth ventricles in CT-scans. 4. Slowly progressive cases are deteriorated by the secondary hydrocephalus. 5. In mild cases hematomas are 3cm or less in diameter on CT-scans and the hematoma evacuation is not indicated for these cases. 6. The shunt operation alone is sufficient for the life saving of the slowly progressive cases, but the hematoma evacuation is indicated in these cases if the functional prognosis is taken into consideration. 7. Immediate hematoma evacuation together with the ventricular drainage is considered to be effective for the life saving of the acute fulminant cases.

Activation of phosphodiesterase in frog rod outer segment by an intermediate of rhodopsin photolysis. II

Frog (Rana catesbeiana) rod outer segment membrane contains cyclic GMP phosphodiesterase (EC 3.1.4.1). Irradiation of dark-adapted rod outer segment membrane increased the enzyme activity by 5-20-fold in the presence of GTP. The phosphodiesterase in rod outer segment membrane is also activated by mixing a photo-product of 11-cis (regenerated), 9-cis or 7-cis rhodopsin which is stable at 0 degrees C. However, neither opsin in the membrane nor all-trans retinal activates the enzyme. The phosphodiesterase in rod outer segment membrane is also activated by irradiation at -4 degrees C. Thus, we conclude that the phosphodiesterase in activated by a common photolysis intermediate of these rhodopsin isomers, perhaps before metarhodopsin II decays.

Activation of phosphodiesterase in frog rod outer segment by an intermediate of rhodopsin photolysis I

Guanosine 3',5'-cyclic monophosphate phosphodiesterase (EC 3.1.4.1) in frog rod outer segment prepared by a sucrose stepwise density gradient method was activated by light in the presence of GTP. Rhodopsin in rod outer segment was solubilized with sucrose laurylmonoester and then purified by concanavalin A-Sepharose column. Addition of photo-bleached preparation of the purified rhodopsin to the crude rod outer segment, which had been prepared by 43% (w/w) sucrose floatation, caused the activation of phosphodiesterase in the dark, while each component of the photo-product eluted from the column (all-trans retinal and opsin) did not. Regenerated rhodopsin prepared from 11-cis retinal and purified opsin activated phosphodiesterase when it was bleached. From these facts it is suggested that an intermediate or a process of photolysis of rhodopsin causes activation of phosphodiesterase.

Photochemical reactions of 13-demethyl visual pigment analogues at low temperatures

The photobleaching reaction of 13-demethylisorhodopsin (hereafter designated as 9-cis- 13-dm-rhodopsin), which was synthesized from 9-cis- 13-demethylretinal and cattle opsin, was investigated by low-temperature spectrophotometry in order to elucidate the role of the 13-methyl group of retinal in photobleaching. When 9-cis- 13-dm-rhodopsin was irradiated at-190 degrees C, batho-13-dm-rhodopsin was produced. Its absorption maximum lay at 532 nm, 11 nm shorter than that of cattle bathorhodopsin (gamma max 543 nm), and batho-13-dm-rhodopsin had an extinction coefficient about 0.6 times that of bathorhodopsin. Batho-13-dm-rhodopsin was thermally unstable. Above-180 degrees C, it converted to a new intermediate, BL-13-dm-rhodopsin, which in turn changed to lumi-13-dm-rhodopsin- above -140 degrees C. BL-13-dm-rhodopsin was "photosensitive" at temperatures around -188 degrees C, though batho-13-dm-rhodopsin and lumi-13-dm-rhodopsin was "photosensitive" at the same temperature. In the photobleaching process, lumi-13-dm-rhodopsin and meta-I-13-dm-rhodopsin were observed. Their thermostabilities were very similar to those of lumirhodopsin and metarhodopsin I, but each dm intermediate differed from its methylated counterpart in its value of gamma max and extinction coefficient.

In vitro metabolism of T-2 toxin in rats

T-2 toxin was rapidly converted in the 9,000 X g supernatant fraction of rat liver homogenate into HT-2 toxin, T-2 tetraol, and two unknown metabolites designated as TMR-1 and TMR-2. TMR-1 was characterized as 4-deacetylneosolaniol (15-acetoxy-3 alpha, 4 beta, 8 alpha-trihydroxy-12,13-epoxytrichothec-9-ene) by spectroscopic analyses. Since the same metabolites were also obtained from HT-2 toxin used as substrate, it was concluded that T-2 toxin was hydrolyzed preferentially at the C-4 position to give HT-2 toxin, which was then metabolized to T-2 tetraol via 4-deacetylneosolaniol. In addition to HT-2 toxin, 4-deacetylneosolaniol and T-2 tetraol, a trace amount of neosolaniol was transformed from T-2 toxin by rat intestinal strips. In vitro metabolic pathways for T-2 toxin in rats are proposed.

Formation of 9-cis- and 11-cis-retinal pigments from bacteriorhodopsin by irradiating purple membrane in acid

Both light-adapted and dark-adapted forms of bacteriorhodopsin in purple membrane in 67% glycerol solution were allowed to stand in acidic conditions by the addition of HCl to final concentrations from 4 X 10(-4) to 2 X 10(-2) M for 24 h at 3 degrees C. Over this concentration range, the acid-induced products from both species showed a maximum absorbance around 600 nm and high-performance liquid chromatography of extracted retinal isomers revealed that the acid-induced form of bacteriorhodopsin has 13-cis- and all-trans-retinals in a molar ratio of 4:6, which is intermediate between those of the dark-adapted and the light-adapted forms at neutral pH values. Exposure of the acid-induced form of bacteriorhodopsin to light at wavelengths longer than 670 nm at 3 degrees C caused a decrease of the absorbance around 600 nm with a concomitant rise of the absorbance around 500 nm. The extract from the irradiated products of bacteriorhodopsin in acid contained 9-cis- and 11-cis-retinals in addition to 13-cis- and all-trans-retinals. The absorbance maximum estimated from the analysis of the absorption spectra and the composition of the isomers was found at 495 nm for the 9-cis-retinal pigment and around 560 nm for the 11-cis-retinal pigment. On irradiation with 438-nm light, the 9-cis-retinal pigment disappeared with a concomitant increase of both the 13-cis- and all-trans-retinal pigments as judged by chromophore analysis and the absorption spectrum. The 9-cis-retinal pigment brought to pH 9 exhibited a maximum absorbance at 450 nm; this could be decomposed by the action of hydroxylamine or converted to a form resembling normal bacteriorhidopsin by 438-nm irradiation.

Circular dichroism of cattle rhodopsin and bathorhodopsin at liquid nitrogen temperatures

The photoevent in vision has been considered to be the conversion of rhodopsin to bathorhodopsin, which is caused by photoisomerization of the chromphoric retinal. Recently some objections were raised to this hypothesis. The reliability of the hypothesis was verified by measurement of circular dichroism of bathorhodopsin. The measurement of circular dichroism of rhodopsin extract (containing 66% or 75% of glycerol) at liquid nitrogen temperatures (-195 degrees C) by a conventional spectropolarimeter induced an extraordinary large signal, owing to linear dichroism originated from conversion of rhodopsin to bathorhodopsin by the measuring light. The similar linear dichrolism can be induced by irradiation of rhodopsin extract at -195 degrees C with polarized light or natural light. At photosteady state the linear dichroism disappeared. Circular dichroism spectrum of cattle rhodopsin displayed two positive peaks ([theta]max = 80 800 degrees at 335 nm, and [theta]max = 42 600 degrees at 500 nm) at -195 degrees C, whereas, bathorhodopsin displayed a positive peak ([theta]max = 43 100 degrees at 334 nm) and a negative peak ([theta]max = 163 000 degrees at 540 nm). The change of the positive sign to negative one at alpha-band of circular dichroism spectrum supports the hypothesis that the conversion of rhodopsin is due to rotation of the chromophoric retinal about C-11--12 double bond ('photoisomerization model').

T-2 metabolites in the excreta of broiler chickens administered 3H-labeled T-2 toxin

A method for the detection of T-2 metabolites was developed and applied to analysis of metabolites in excreta of broiler chickens administered 3H-labeled T-2 toxin. The method used acetonitrile extraction and partitioning with petroleum ether followed by chromatography on Amberlite XAD-2, Florisil, and Sep-Pak C18. The recovery of T-2 toxin added to the chicken excreta was 73% at a concentration of 0.2 microgram/g. About 80% of orally administered 3H-labeled T-2 toxin was rapidly metabolized to more polar derivatives and eliminated in the excreta within 48 h. T-2 toxin, HT-2 toxin, neosolaniol, and T-2 tetraol were detected at 0.06 to 1.13% of the total dose, 48 h after administration. Eight unknown derivatives, named TB-1 to TB-8, were quantitatively more significant than the metabolites above. TB-3 and TB-9 represented about 12 and 25% of the total dose, respectively. One of the metabolites (TB-6), 1.5% of the total dose, was identified as 4-deacetylneosolaniol (15-acetyl-3 alpha, 4 beta, 8 alpha-trihydroxy-12, 13-epoxytrichothec-9-ene).