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P Scherrer

Publications and source records attributed to P Scherrer.

At least 37 records · Page 2Linked to original sources
PubMed1989

Retinal isomer ratio in dark-adapted purple membrane and bacteriorhodopsin monomers.

On the basis of data obtained by spectroscopic analysis and chromatography of retinal extracts, a consensus has been adopted that dark-adapted purple membrane (pm) contains 13-cis- and all-trans-retinal in equal amounts, whereas the light-adapted membrane contains all-trans-retinal only. We have developed an improved extraction technique which extracts up to 70% of the retinal in pm within 4 min. In the extracts from dark-adapted pm at room temperature, we consistently find 66-67% 13-cis-retinal and 33-34% all-trans-retinal, and more than 98.5% all-trans isomer in light-adapted samples. The spectrum obtained by reconstitution of bacterioopsin with 13-cis-retinal at 2 degrees C (to minimize isomerization) shows an absorbance maximum at 554 nm and agrees well with the spectrum for the 13-cis component calculated from the dark-adapted and light-adapted bR spectra with our extraction data. The ratio of 13-cis:all-trans isomer in dark-adapted pm is 2:1 and nearly constant between 0 and 38 degrees C but begins to decrease distinctly above 40 degrees C, and more rapidly near 70 degrees C, reaching 0.75 at 90 degrees C. The van't Hoff plot of the isomer ratio shows a nonlinear temperature dependence above 40 degrees C, indicating a more complex system than a simple thermal 13-cis/all-trans isomer equilibrium. We attribute the broadening, absorbance decrease, and blut shift of the visible absorption band with increasing temperature to the appearance of at least one and possibly two or three new chromophores which contain, mainly or exclusively, the all-trans isomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriorhodopsins↗
PubMed1987

Tyrosine and carboxyl protonation changes in the bacteriorhodopsin photocycle. 2. Tyrosines-26 and -64.

Low-temperature Fourier transform infrared (FTIR) and UV difference spectroscopies combined with selective tyrosine nitration and tyrosine isotopic labeling have been used to investigate the participation of tyrosines-26 and -64 in the bacteriorhodopsin (bR) photocycle. Nitration of Tyr-26 has no detectable effect on the FTIR or UV difference spectra of the BR570----K630 or BR570----M412 transitions. In contrast, nitration of Tyr-64 causes changes in both the FTIR and UV spectra of these transitions. However, this nitration does not alter tyrosine peaks in the FTIR difference spectra which have previously been associated with the protonation of a tyrosinate by K630 and the deprotonation of a tyrosine by M412 [Roepe, P., Ahl, P. L., Das Gupta, S. K., Herzfeld, J., & Rothschild, K. J. (1987) Biochemistry (preceding paper in this issue)]. Instead, Tyr-64 nitration appears to affect other tyrosine peaks. These results and changes in UV difference spectra upon Tyr-64 nitration are consistent with the deprotonation of Tyr-64 by M412 as concluded previously [Scherrer, P., & Stoeckenius, W. (1985) Biochemistry 24, 7733-7740]. Effects on chromophore vibrations caused by Tyr-64 nitration are unaltered upon reducing the nitrotyrosine to aminotyrosine with sodium dithionite. Finally, nitro-Tyr-64 causes a shift in the frequency of a positive peak at 1739 cm-1 in the BR570----M412 FTIR difference spectrum which reflects the protonation of a carboxyl-containing residue [Engelhard, M., Gerwert, K., Hess, B., Kreutz, W., & Siebert, F. (1985) Biochemistry 24, 400-407; Roepe, P., Ahl, P. L., Das Gupta, S. K., Herzfeld, J., & Rothschild, K. J. (1987) Biochemistry (preceding paper in this issue)]. The shift does not occur for samples containing amino-Tyr-64. These data suggest that Tyr-64 may interact with this carboxyl group.

Bacteriorhodopsins↗
PubMed1987

Biochemical and spectroscopic characterization of the blue-green photoreceptor in Halobacterium halobium.

Spectroscopic evidence indicates the presence of a second sensory receptor sR-II in Halobacterium halobium, which causes a repellent response to blue-green light. Reactions with hydroxylamine and NaCNBH3 and reconstitution of the bleached pigment with retinal show that it is very similar to the other retinylidene pigments bacteriorhodopsin, halorhodopsin, and especially the earlier-discovered phototaxis receptor, sensory rhodopsin, renamed sR-I587. The second sensory receptor, sR-II480, has an absorbance maximum at 480 nm and undergoes a cyclic photoreaction with a half-time of approximately 200 msec. Its predominant photocycle intermediate absorbs maximally near 360 nm. The receptor can be detected spectroscopically in the presence of sR-I587 and quantitated through its transient response to 450-nm excitation. It is selectively bleached by low hydroxylamine concentrations that are insufficient to bleach sR-I587 significantly. Its photochemical and phototactic activities can be restored by addition of retinal. The mobility of the receptor, on NaDodSO4/polyacrylamide gels, was similar or identical to that of sR-I587 and slightly faster than bacteriorhodopsin, yielding an apparent molecular mass of 23-24 kDa.

Bacteriorhodopsins↗
PubMed1987

[Severe mental disorders and the problem of hospitalization].

The problem of the hospitalization of patients with severe mental disorders. In relating three clinical cases, the author's purpose is to show that sometimes an hospitalization of long duration is necessary and that the psychiatrist has to be able to assume that decision for the patient's sake. In the first two cases, suicide was the issue, each time after a too-short period of hospitalization, given the antecedents in the first case, and in the second, not allowing that an efficient treatment be set up and accepted. The third case shows how a sufficiently long hospitalization (about 2 months) could enable the setting of a long-duration treatment which led to a sensible improvement of the patient's state.

Adult↗
PubMed1986

[Prevention of acute renal insufficiency due to nontraumatic rhabdomyolysis].

Nine patients with nontraumatic rhabdomyolysis underwent preventive treatment for acute renal failure (ARF) (vascular filling, furosemide, dopamine, Na bicarbonate, allopurinol). Four patients developed functional azotemia and 4 others ARF with conserved diuresis and normalization of renal function without substitutive treatment. Only one patient remained oligoanuric and needed hemodialysis for 3 weeks. Comparing these 3 groups it appears that the severity of the renal impairment is due on one hand to the extent of the muscular lysis and on the other to early commencement of preventive treatment.

Acute Kidney Injury↗
PubMed1986

Color discrimination in halobacteria: spectroscopic characterization of a second sensory receptor covering the blue-green region of the spectrum.

Halobacterium halobium is attracted by green and red light and repelled by blue-green and shorter wavelength light. a photochromic, rhodopsin-like protein in the cell membrane, sensory rhodopsin sR587, has been identified as the receptor for the long-wavelength and near-UV stimuli. Discrepancies between the action spectrum for the repellent effect of blue light and the absorption spectrum of sR587 and its photocycle intermediate S373 strongly suggest the existence of an additional photoreceptor for the blue region of the spectrum. Transient light-induced absorbance changes in intact cells and cell membranes show, in addition to sR587, the presence of a second photoactive pigment with maximal absorption near 480 nm. It undergoes a cyclic photoreaction with a half-time of 150 msec. One intermediate state with maximal absorption near 360 nm has been resolved. The spectral properties of the new pigment are consistent with a function as the postulated photoreceptor for the repellent effect of blue light. The phototactic reactions and both pigments are absent when retinal synthesis is blocked; both can be restored by the addition of retinal. These results confirm and extend similar observations by Takahashi et al. [Takahashi, T., Tomioka, H., Kamo, N. & Kobatake, Y. (1985) FEMS Microbiol. Lett. 28, 161-164]. The archaeobacterium H. halobium thus uses two different mechanisms for color discrimination; it uses two rhodopsin-like receptors with different spectral sensitivities and also the photochromicity of at least one of these receptors to distinguish between three regions covering the visible and near-UV spectrum.

Bacteriorhodopsins↗
PubMed1985

Effects of tyrosine-26 and tyrosine-64 nitration on the photoreactions of bacteriorhodopsin.

In the dark, all titratable tyrosine residues of bacteriorhodopsin have pK's of greater than 11.0, which may be caused by the hydrophobic environment for buried residues and by high negative charge density for surface residues [Scherrer, P., & Stoeckenius, W. (1984) Biochemistry 23, 6195-6202]. Under illumination, deprotonation of only one tyrosine is observed in the micro- and millisecond time ranges of the photocycle; this is Tyr-64. Nitration of Tyr-64 decreases the chromophore absorbance, shifts the absorption maximum to 535 nm, and affects photocycle kinetics. However, restoring its native pK by reduction after nitration has no effect on the changes in photocycle kinetics or absorbance of the chromophore. Nitration of Tyr-64 apparently causes a conformational change in bR, which is independent of the pK of its phenolic group. These observations contradict earlier conclusions that in the photocycle a tyrosine residue directly interacts with the Schiff base during its deprotonation or reprotonation. The protonation state of Tyr-26 and the alkaline chromophore transition are correlated, as shown earlier (Scherrer & Stoeckenius, 1984). Lowering the pK of Tyr-26 by nitration decreases the M-decay rate, and this effect is partially reversed by reduction of the nitro group. We conclude that Tyr-26 may be located close to the chromophore and interact with it; but its protonation state does not change at physiological pH and in the microsecond time range of the photocycle. Tyr-64 is apparently located at or close to the external surface; its modification strongly affects the chromophore but apparently indirectly and not through its protonation changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1985

[Myocardial involvement in nontraumatic rhabdomyolysis following an opiate overdose].

Eight young addicts developed rhabdomyolysis as a complication of heroin overdose. ECG, plasma enzyme time activity curves and thallium myocardial scintigraphy were highly suggestive of a myocardial lesion associated with rhabdomyolysis. Such changes were particularly striking in 3 patients with acute left ventricular failure, as shown by a hemodynamic investigation (3 patients) and by echocardiography (1 patient). All patients recovered but myocardial scintigraphy and ECG remained abnormal for a period ranging from 8 months to 3 years following the acute episode. Although associated metabolic changes may play a role in myocardial dysfunction, the most likely mechanism appears to be a direct toxic effect of heroin on cardiac muscle.

Adult↗
PubMed1984

Selective nitration of tyrosines-26 and -64 in bacteriorhodopsin with tetranitromethane.

Nitration of tyrosine-26 at pH 9.0 in bacteriorhodopsin does not change its absorption spectrum but lowers the apparent pK of the alkaline transition to a blue-shifted chromophore from about pH 12.0 to 10.6. This effect is reversed by reducing the nitrotyrosine-26 to aminotyrosine which demonstrates that the protonation state of tyrosine-26 and the alkaline chromophore transition are correlated. Nitration of tyrosine-64 resulted in a shift of the purple complex from 570 to 535 nm at neutral pH. The alkaline transition pK of such a nitrated membrane was below 10 but was clearly independent of the protonation state of tyrosine-64 because it is not reversed by reduction of the nitrotyrosine. Nitrotyrosine-26 showed spectral properties similar to L-nitrotyrosine in aqueous environment while nitrotyrosine-64 showed only a 360-nm absorbance in the apomembrane but not in the retinal-containing membrane. Both tyrosines are accessible to water-soluble reagents.

Bacteriorhodopsins↗
PubMed1984

[A case of Whipple disease with a pseudotumorous presentation: differential diagnosis with mesenteric panniculitis].

A case of Whipple's disease initially presenting as an inflammatory, granulomatous and pseudotumorous infiltration of the mesenterium is discussed. The initial diagnosis of mesenteric panniculitis was invalidated by the typical histological findings of Whipple's disease in a duodenal biopsy performed 18 months later for malabsorption syndrome. This case illustrates the difficulties besetting differential diagnosis of inflammatory and granulomatous lesions of the mesenterium.

Diagnosis, Differential↗
PubMed1984

[The place of kidney biopsies in the diagnosis of isolated hematuria].

Twenty-six patients with idiopathic hematuria, i.e. with normal intravenous pyelography, without arterial hypertension, renal failure or significant proteinuria, underwent renal biopsy in our institution between 1973 and 1981. Segmental proliferative endocapillary glomerulonephritis was diagnosed in 13 cases; in the other 13 patients the renal tissue was either normal (6) or presented only minor lesions of the mesangium (5) or interstitial tissue (2). Twenty-two patients underwent a follow-up examination after a mean of 51 months (range 12-120). The hematuria had disappeared in half of them and no patients had developed hypertension or renal failure. These results suggest that in cases of idiopathic hematuria renal biopsy is not indicated for prognostic or therapeutic reasons, though in some cases it may avoid repeated and potentially dangerous investigations.

Adolescent↗