Magic angle sample spinning 13C nuclear magnetic resonance of isotopically labeled bacteriorhodopsin

Bacteriorhodopsin (bR), the light-driven proton pump protein from Halobacterium halobium, was biosynthetically labeled with [4-13C]Asp. The incorporation yield was 48%. The magic angle sample spinning (MASS) 13C nuclear magnetic resonance (NMR) spectrum of this sample revealed six different peaks superimposed on a broad band of naturally abundant peptide-bond 13C. Two of the six carbonyl signals can be attributed to internal-protonated Asp carboxyl groups, one of which might be Asp115. An additional resonance at 110 ppm can be associated with the C-11 carbon of Trp, indicating an unusual biosynthetic pathway of this amino acid in Halobacterium halobium. Similar measurements performed on papain-treated purple membrane which lacks the C-terminal tail display two new intense signals at 178 and 178.9 ppm. If the same spectrum is taken without cross-polarization, these signals do not decrease or disappear. On the basis of their intensities and their chemical shifts, one can assign in addition to the C-terminal Asp four Asp residues facing the cytoplasmic phase. In native bR, at least two of these form a salt-bridge-like bond which also might include the C-terminal tail. These experiments not only provide data about the chemical environment of the Asp residues within the hydrophobic core of bacteriorhodopsin but also yield information about the interactions between surface components.

Curvature and Propagation Velocity of Chemical Waves

The collision of circular chemical waves in an excitable medium, the Belousov-Zhabotinskii reaction, leads to characteristic cusplike structures. The high curvatures of these structures are especially suitable for experimentally verifying the predicted proportionality between the velocity and the shape of traveling waves. A computerized spectrophotometric video technique with microscopic resolution was used to determine the proportionality factor (2 x 10(-5) square centimeter per second), which in this case is the diffusion coefficient of the autocatalytic species of the reaction system. A numerical calculation of the spatiotemporal evolution of the cusp structure is in good agreement with the experimental observations.

A rapid population method for action spectra applied to Halobacterium halobium

We have developed a simple and rapid technique for measuring the action spectra for phototaxis of populations of microorganisms and applied it to halobacteria. A microscope with a dark-field condenser was used to illuminate the cell suspension in a sealed chamber with light of wavelength greater than 750 nm; in this region of the spectrum, the halobacteria show no phototactic response. A 150-micron spot of light from a xenon arc lamp, whose wavelength and intensity can be varied, was projected through the objective lens into the center of the dark field. The objective lens imaged this measuring spot through a 780-nm cut-off filter on an aperture in front of a photomultiplier. The intensity of the scattered 750-nm light, and therefore the photomultiplier current, is proportional to the number of cells in the measuring spot. A third lamp provided background light of variable wavelength and intensity through the dark-field condenser. To minimize secondary effects due to large changes in cell density, we recorded the initial changes in the photomultiplier current over 1 min after the actinic light had been switched on. By plotting the rate of change against wavelength, we obtained action spectra after the proper corrections for changes in light intensity with wavelength were applied and saturation effects were avoided.

Inhibition of yeast mitochondrial F1-ATPase, F0F1-ATPase and submitochondrial particles by rhodamines and ethidium bromide

ATP hydrolysis by F1-ATPase is strongly inhibited by cationic rhodamines; neutral rhodamines are very poor inhibitors. Rhodamine 6G is a noncompetitive inhibitor of purified F0F1-ATPase and submitochondrial particles, however, an uncompetitive inhibitor of F1-ATPase (KI approximately equal to 2.4 microM for all three enzyme forms). Ethidium bromide is a noncompetitive inhibitor of F0F1-ATPase, submitochondrial particles and also F1-ATPase (KI approximately equal to 270 microM). Neither of the inhibitors affects the negative cooperativity (nH approximately equal to 0.7). The non-identical binding sites for rhodamine 6G and ethidium bromide are located on the F1-moiety and are topologically distinct from the catalytic site. Binding of the inhibitors prevents the conformational changes essential for energy transduction. It is concluded that the inhibitor binding sites are involved in proton translocation. In F1-ATPase, binding of MgATP at a catalytic site causes conformational changes, which allosterically induce the correct structure of the rhodamine 6G binding site. In F0F1-ATPase, this conformation of the F1-moiety exists a priori, due to allosteric interactions with F0-subunits. The binding site for ethidium bromide on F1-ATPase does not require substrate binding at the catalytic site and is not affected by F0F1-subunit interactions.

Three-dimensional representation of chemical gradients

Perspective display techniques are applied to chemical and biochemical data sets. These represent spatially distributed gradients of reactive compounds that participate in pattern-formation processes due to reaction-diffusion or reaction-convection coupling. The patterns form in thin solution layers and are observed as chemical waves in the Belousov-Zhabotinskii reaction, as convection-induced stationary structures during oscillating glycolysis in yeast cytoplasm, and as the diffusive spreading of enzyme-catalyzed metabolic turnover in a substrate layer. The digital data are measured with a two-dimensional spectrophotometer based on a computerized video equipment with high spatial, temporal and intensity resolution. By application of three-dimensional procedures detailed structural properties of chemical and biochemical model systems will be presented yielding localization of reaction and transport events.

[Idiopathic hypercalciuria--recent pathogenetic and diagnostic aspects]

The term "hypercalciuria" is not uniformly applied. Recent investigations show that the upper normal limits of 24-hour calciuria are above the originally defined 7.5 mmol in men in 6.25 mmol in women. There is no clear evidence that 24-hour calciuria is more often increased in idiopathic calcium stone formers than in healthy controls with normal calcium metabolism. Because of a disordered regulation of 1,25-dihydroxy-vitamin D3-production, the serum-1,25-dihydroxy-vitamin D3 is increased in idiopathic calcium stone formers. A calcium loading test during undisturbed individual calcium homeostasis reveals increased intestinal calcium absorption in calcium stone formers. Metabolic evaluations are often not performed under the same conditions as those in which the stone formation occurred. As long as the primary metabolic defect has not been identified, classification into "absorptive" and "renal hypercalciuria" does not seem to be justified.

[Peroral calcium administration test with free diet in idiopathic calcium nephrolithiasis--possibilities and limits]

Seventeen patients who recurrently formed idiopathic calcium kidney stones (SF) and 25 age- and sex-matched healthy blood donors (H) were challenged by an oral calcium load (1 g) after an overnight fast. Their usual diet was not changed before the test. Urine samples were taken before, 2 1/2, and 4 h after the calcium load. A blood sample was drawn 3 3/4 h after calcium loading. Before and 2 1/2 h after calcium dosage urinary measurements of calcium, magnesium, phosphate, oxalate, uric acid, and creatinine did not reveal any differences between SF and H. According to the calciuria after 4 h SF were separated in normocalciurics (NCSF) and hypercalciurics (HCSF). Nine-tenths of the NCSF had higher serum ionic calcium levels than H after calcium load (P less than 0.001), whereas HCSF were not different from H. Serum phosphate in SF was lower than in H (P less than 0.001). Carboxy-terminal parathormone, measured in 3 NCSF and 2 HCSF, was normal. Depending on the calciuria or calcemia 4 h after an oral calcium load, 16 of 17 SF showed a metabolic abnormality (hypercalcemia or hypercalciuria). It is concluded that intestinal calcium absorption in SF might be increased to variable rates.

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.

[Severe electrolyte disorders during the therapy of heart failure with the therapy of heart failure with the ACE-inhibitor enalapril]

Angiotensin I converting enzyme inhibition by captopril and enalapril may influence sodium and potassium homeostasis. In patients without cardiac failure and with normal renal function significant electrolyte disturbances rarely occur. We report on four patients who developed life-threatening electrolyte disturbances following treatment with enalapril for severe cardiac failure (NYHA-class II-IV). There were important concomitant factors in all four cases: in one case under additional medication with a thiazide diuretic and a nonsteroidal antiinflammatory, hyponatremia of 107 mmol/l occurred. In two further cases severe hyperkalemia of 7.4 and 7.3 mmol/l was observed in the presence of acute renal failure due to enalapril-induced hypotension and concomitant therapy with a nonsteroidal antiinflammatory drug respectively. In a fourth case the combination of enalapril with a potassium-sparing diuretic provoked severe hyperkalemia of 7.9 mmol/l.

[Questionable significance of the chemical analysis of a single 24-hour urine sample in recurrent calcium oxalate nephrolithiasis]

Chemical findings were obtained from 24 h urine samples of 43 male calcium-oxalate stone-formers on an unrestricted diet. Results were compared with data from 51 age-matched healthy blood donors. No differences were found in the excreted quantities of calcium, oxalic acid, uric acid and inorganic phosphate, nor in the calcium to creatinine ratio or the activity product of calcium and oxalic acid. The only differences were a higher output of magnesium and a higher magnesium to calcium ratio for controls. The extent of these differences, however, does not justify further subdivision of the group of stone-formers. The diagnostic and therapeutic significance of the chemical analysis of one 24 h urine sample is doubtful for this group of patients.

Two-dimensional spectrophotometry and pseudo-color representation of chemical reaction patterns

The formation of spatio-temporal patterns in layers of chemical and biochemical media is observed and quantified by a two-dimensional spectrophotometer based on a computerized video equipment with high spatial, temporal, and intensity resolution. Images are shown, to some extent, in pseudo-colors. The use of pseudo-colors and three-dimensional perspective representations enhances the perception of the information contained in an image and the inherent order of the spatial structures.

Input-response relationships in the dynamics of glycolysis

The dynamic response of glycolysis is investigated using a two-enzyme model with three different type of input flux time dependences: constant, sinusoidal, and amplitude or frequency modulated (AM or FM) input flux. The analysis reveals that the system acts as a device which transduces amplitudes and frequencies of the input function into complex and remarkably diverse response patterns. This device may have more than one response possibilities for a single input function, owing to the coexistence of attractors in phase space. In such a case one response function can be switched over into the other by short substrate pulses. Stroboscopic plots reveal that chaotic regimes obtained under sinusoidal input flux obey a stretch-fold-press process, similar to the baker's transformation, upon a change of the stroboscoping phase. Chaotic oscillations obtained under AM or FM conditions often show a much higher degree of randomness than those obtained under sinusoidal input. This is expressed quantitatively by an enhanced Liapunov dimension of the attractors.

Cytochemical localization of alkaline phosphatase in the cell membrane of Dictyostelium discoideum amebae

We demonstrated that alkaline phosphatase was localized on the cell membrane of Dictyostelium discoideum amebae and on isolated plasma membranes. The enzyme activity was specifically inhibited by 0.01 M KCN or cysteine. The same method could also be applied to baker's yeast and MDCK cells (dog kidney cells in vitro).

Two-dimensional spectrophotometry with high spatial and temporal resolution by digital video techniques and powerful computers

A two-dimensional spectrophotometer having a spatial raster resolution of 512 X 512 picture elements with 256 grey levels and a time resolution of 30 images per min is assembled by combination of digital video techniques and a powerful computer system. The instrument is applied to the analysis of pattern formation processes in cytoplasmic media.

alpha, beta-Bidentate CrADP abolishes the negative cooperativity of yeast mitochondrial F1-ATPase

The hydrolysis of MgATP and MgITP by mitochondrial F1-ATPase from Saccharomyces cerevisiae is competitively inhibited by alpha, beta-CrADP, alpha, beta, gamma-CrATP and beta, gamma-CrATP. The apparent K1 values of the three complexes are in the range of the half-saturating MgATP concentration. The negative cooperativity (nH = 0.7) of MgATP hydrolysis is totally abolished by alpha, beta-CrADP (nH = 1.0), while it is not affected by the CrATP. It is concluded that alpha, beta-CrADP binds exclusively at the regulatory site and that CrATP binds exclusively to the catalytic site.

Light-driven protonation changes of internal aspartic acids of bacteriorhodopsin: an investigation by static and time-resolved infrared difference spectroscopy using [4-13C]aspartic acid labeled purple membrane

The molecular events during the photocycle of bacteriorhodopsin have been studied by the method of time-resolved and static infrared difference spectroscopy. Characteristic spectral changes involving the C=O stretching vibration of protonated carboxylic groups were detected. To identify the corresponding groups with either glutamic or aspartic acid, BR was selectively labeled with [4-13C]aspartic acid. An incorporation of ca. 70% was obtained. The comparison of the difference spectra in the region of the CO2- stretching vibrations of labeled and unlabeled BR indicates that ionized aspartic acids are influenced during the photocycle, the earliest effect being observed already at the K610 intermediate. Taken together, the results provide evidence that four internal aspartic acids undergo protonation changes and that one glutamic acid, remaining protonated, is disturbed. The results are discussed in relation to the various aspects of the proton pumping mechanism, such as retinal isomerization, charge separation, pK changes, and proton pathway.

Activation of yeast 6-phosphofructo-2-kinase by protein kinase and phosphate

6-Phosphofructo-2-kinase (PFK2) is activated by a cAMP-dependent protein kinase, and inactivated by phosphatase, indicating the interconversion of PFK2. Inorganic phosphate also activates PFK2, and the optimum pH for the PFK2 activity varies with the concentration of phosphate. Phosphate also enhances the inactivation of PFK2 by citrate, suggesting that phosphate acts as a regulator of PFK2.

Characterization of high density lipoprotein binding activity in rat adrenocortical cells

Rat adrenocortical cells take up high density lipoprotein cholesterol for use as steroidogenic substrate. To better understand this unique uptake process, we have first characterized HDL binding. Infusion of human 125I-labeled HDL into rats pretreated with 4-APP demonstrated that the adrenal and ovary accumulate HDL in a saturable fashion in vivo. Subsequent studies using isolated rat adrenocortical cells demonstrated that cellular uptake of HDL is comprised of two events. One event is characterized by reversible membrane binding and is complete by 60 min (t1/2 = 20 min). The second event is marked by irreversible apoprotein accumulation which continues for at least 3 hr. Reversibly bound material exhibits the same apoprotein distribution as unincubated HDL. Irreversible accumulation could not be attributed to internalization or lysosomal accumulation inasmuch as it also occurred with partially purified plasma membranes and was not enhanced by addition of chloroquine. Reversible binding of human HDL3 exhibited a saturable dependence on concentration (Kd = 27 micrograms protein/ml; N = 3.0 X 10(6) sites/cell) similar to that previously reported for rat liver, ovary, and testis. Cell accumulation of HDL decreased by over 80% at 4 degrees C compared to 37 degrees C, did not require calcium, and was not diminished by prior cell treatment with trypsin or pronase. These results indicate that rat adrenocortical cells possess plasma membrane recognition sites for HDL with different properties than those of the LDL receptor. Moreover, adrenal accumulation of HDL apoproteins does not lead to secondary lysosome formation.