Microbial acetyl conjugation of T-2 toxin and its derivatives

The acetyl conjugation of T-2 toxin and its derivatives, the 12,13-epoxytrichothecene mycotoxins, was studied by using mycelia of trichothecene-producing strains of Fusarium graminearum, F. nivale, Calonectria nivalis, and F. sporotrichoides, T-2 toxin was efficiently converted into acetyl T-2 toxin by all strains except a T-2 toxin-producing strain of F. sporotrichoides, which hydrolyzed the substrate to HT-2-toxin and neosolaniol. HT-2 toxin was conjugated to 3-acetyl HT-2 toxin as an only product by mycelia of F. graminearum and C. nivalis, but was also resistant to conjugation by both F. nivale and F. sporotrichoides. Neosolaniol was also biotransformed selectively into 3-acetyl neosolaniol by F. graminearum. However, 3-acetyl HT-2 toxin was not acetylated by any of the strains under the conditions employed, but was hydrolyzed to HT-2 toxin by F. graminearum and F. nivale. This is the first report on the biological 3 alpha-O-acetyl conjugation of T-2 toxin and its derivatives.

Photochemical studies of 7-cis-rhodopsin at low temperatures. Nature and properties of the bathointermediate

The photoreaction of 7-cis-rhodopsin derived from 7-cis-retinal and cattle opsin was studied by low-temperature spectrophotometry. Upon irradiation of 7-cis-rhodopsin at liquid nitrogen temperature (-190 degrees C) with blue light, its spectrum shifted to the longer wavelengths, indicating the formation of a bathoproduct. The bathoproduct thus formed was found to be identical with bathorhodopsin formed from rhodopsin in their spectroscopic, photochemical, and thermal properties. Therefore, we believe that the bathoproduct is, in fact, bathorhodopsin. The fact that 7-cis-rhodopsin can be readily converted to rhodopsin and to 9-cis-rhodopsin shows that the identical retinal binding site of opsin is involved in the three isomeric rhodopsins. These results appear to be consistent with the notion that the chromophore of bathorhodopsin is a twisted all-trans isomer, which is readily obtainable from the 7-cis, 9-cis, and 11-cis isomers.

Light-induced pigment aggregation in cultured fish melanophores: spectral sensitivity and inhibitory effects of theophylline and cyclic adenosine-3′,5′-monophosphate

About 20% of xiphophorin fish (Xiphophorus maculatus) dermal melanophores which were cultured in monolayer for 5 to 10 days responded to light directly, exhibiting reversible melanosome aggregation within a few minutes. In order to determine the spectral sensitivity for the light-response, absorbance changes due to the light-induced melanosome aggregation were measured on single melanophores in a range of wavelengths from 370 to 550 nm using a recording microspectrophotometer. The melanophores showed maximum sensitivity to a wavelength of about 410 nm and very little to those longer than 500 nm. 10(−4) to 10(−2) M theophylline and 10(−4) M cAMP had inhibitory effects on the light-response.

Photochemical reaction of 9-cis-retro-gamma-rhodopsin at low temperatures

9-cis-Retro-gamma-rhodopsin (lambda max = 420 nm) was prepared from 9-cis-retro-gamma-retinal and cattle opsin. After cooling to liquid nitrogen temperature (77 K), the pigment was irradiated with light at 380 nm. The spectrum shifted to the longer wavelengths, owing to formation of a batho product. This fact indicates that the conjugated double bond system from C-5 to C-8 of the chromophoric retinal in rhodopsin was not necessary for formation of bathorhodopsin. Reirradiation of the batho product with light at wavelengths longer than 520 nm yielded a mixture composed of presumably 9- or 11-cis forms of retro-gamma-rhodopsin. These three isomers are interconvertible by light at liquid nitrogen temperature. Thus the retro-gamma-rhodopsin system is similar in photochemical reaction at 77 K to cattle rhodopsin system. Each system has its own batho product. Based on these results, it was infered that the formation of batho-rhodopsin is due to photoisomerization of the chromophoric retinal of rhodopsin and is not due to translocation of a proton on the ring or on the side chain from C-6 to C-8 of the chromophoric retinal to the Schiff-base nitrogen.

Formation of 7-cis- and 13-cis-retinal pigments by irradiating squid rhodopsin

Squid rhodopsin was irradiated with orange light (greater than 530 nm) at various temperatures from -190 to 10 degrees C until a photo-steady-state mixture was formed. Then the chromophoric retinals were extracted from the photo-steady-state mixtures and their isomer composition was analyzed by high-performance liquid chromatography. In the case of photo-steady-state mixture formed at -85 degrees C, large peaks in the chromatogram were found at the positions of both 7-cis- and 13-cis-retinals. Each peak was further identified by synthesizing the pigments from these retinals with cattle opsin or apobacteriorhodopsin. Both 7-cis- and 13-cis-retinals were also extracted from a photo-steady-state mixture formed by irradiation at -40, at 0, or at 10 degrees C. These isomers were scarcely detected in a photo-steady-state mixture formed by irradiation at -190 degrees C, though 9-cis-retinal was found as a major constituent in this mixture. Irradiation of lumirhodopsin at -190 degrees C, however, produced 7-cis-retinal pigment. These findings suggest that bathorhodopsin may have a conformation to prevent the formation of 7-cis-retinal from the all-trans form and that this particular conformation may be relaxed by the conversion of bathorhodopsin to lumirhodopsin.

Circular dichroism of squid rhodopsin and its intermediates

Circular dichroism (CD) and absorption spectra of squid (Todarodes pacificus) rhodopsin, isorhodopsin and the intermediates was measured at low temperatures. Squid rhodopsin has positive CD bands at wavelengths corresponding the alpha- and beta-absorption bands at liquid nitrogen temperature (CD maxima: 485 nm at alpha-band and 348 nm at beta-band) as well as at room temperature (CD maxima: 474 nm at alpha-band and 347 nm at beta-band). The rotational strength of the alpha-band has a molecular ellipticity about twice that of cattle rhodopsin. The CD spectrum of bathorhodopsin displays a negative peak at 532 nm, the rotational strength of which has an absolute value slightly larger than that of rhodopsin. The reversal in sign at alpha-band of the CD spectrum may indicate that the isomerization of retinal chromophore from twisted 11-cis form to twisted 11-trans form has occurred in the process of conversion from rhodopsin to bathorhodopsin. Lumirhodopsin has a small negative CD band at 490 nm, the maximum of which lies at 25 nm shorter wavelengths than the absorption maximum (515 nm), and a large positive CD band near 290 nm, which is not observed in rhodopsin and the other intermediates. This band may de derived from a conformational change of the opsin. In the process of changing from lumirhodopsin to LM-rhodopsin, The CD bands at visible and near ultraviolet regions disappear. Both alkaline and acid metarhodopsins have no CD bands at visible and near ultraviolet regions.

Formation of hyposorhodopsin in frog retina

Hypsorhodopsin was formed in frog retina by irradiation at liquid helium temperature and converted into bathorhodopsin above about 29K.

Formation of 7-cis retinal by the direct irradiation of all-trans retinal

7-cis Retinal, one of the geometrical isomers of retinal, was prepared by the direct irradiation of all-trans retinal dissolved in ethanol and successive separation by high performance liquid chromatography. The production for its purification and identification are described.

Isomeric composition of retinal chromophore in dark-adapted bacteriorhodopsin

1. Retinal isomers extracted from the acid-hydrolysate of cetyltrimethylammonium bromide-treated dark-adapted bacteriorhodopsin (bRD) were analyzed in a high performance liquid chromatograph (HPLC) system. The extract from bRD contains almost equal molar amounts of both 13-cis retinal and all-trans retinal isomers. The extent of isomerization and the yield of both isomers during the isolation process were investigated by the application of the same extraction procedure to artificial bacteriorhodopsin reconstituted with 13-cis retinal isomer (13-cis bacteriorhodopsin) and also to light-adapted bacteriorhodopsin (bRL) which has been shown to contain only the all-trans isomer (all-trans bacteriorhodopsin). 2. A reconstituted bacteriorhodopsin, which had been prepared from apo-bacteriorhodopsin and an equimolar mixture of both 13-cis retinal and all-trans retinal isomers, showed an absorption spectrum having the same maximum wavelength as that of bRD even at the beginning of the reconstitution process. 3. Analysis of the photosteady states of bRD at -190 degrees C revealed that it was composed of two different species, one having 13-cis retinal and the other having all-trans retinal isomers in approximately equal molar amounts. These two also gave their respective photoproducts. 4. From these results it can be concluded that bRD contains both 13-cis retinal and all-trans retinal isomers in nearly equal molar amounts as its chromophore.

Emetic and refusal activity of deoxynivalenol to swine

The minimum emetic dose of deoxynivalenol to swine weighing 9 to 10 kg was 0.05 mg/kg of body weight intraperitoneally and 0.1 to 0.2 mg/kg orally. There was no emesis by undosed pigs consuming vomitus from pigs orally dosed with deoxynivalenol or penned with such pigs without access to vomitus. Analysis by gas-liquid chromatography of a sample of Gibberella zeae-infected corn containing about 25% visually damaged kernels indicated 12 ppm of deoxynivalenol. Deoxynivalenol added to feed reduced feed consumption of 20- to 45-kg pigs, ranging from a 20% decrease with 3.6 ppm to 90% reduction with 40 ppm. Loss in weight was associated with feed refusal. Feed refusal, however, was much greater for naturally infected corn samples than for feeds with equal concentrations of the pure compound added, indicating the involvement of an additional factor(s) in the swine refusal response.