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H Scheer

Publications and source records attributed to H Scheer.

At least 37 records · Page 2Linked to original sources
PubMed1990

Infrared spectroscopy of phytochrome and model pigments.

Fourier-transform infrared difference spectra between the red-absorbing and far-red-absorbing forms of oat phytochrome have been measured in H2O and 2H2O. The difference spectra are compared with infrared spectra of model compounds, i.e. the (5Z,10Z,15Z)- and (5Z,10Z,15E)-isomers of 2,3,7,8,12,13,17,18-octaethyl-bilindion (Et8-bilindion), 2,3-dihydro-2,3,7,8,12,13,17,18-octaethyl-bilindion (H2Et8-bilindion), and protonated H2Et8-bilindion in various solvents. The spectra of the model compounds show that only for the protonated forms can clear differences between the two isomers be detected. Since considerable differences are present between the spectra of Et8-bilindion and H2Et8-bilindion, it is concluded that only the latter compound can serve as a model system of phytochrome. The 2H2O effect on the difference spectrum of phytochrome supports the view that the chromophore in red-absorbing phytochrome is protonated and suggests, in addition, that it is also protonated in far-red-absorbing phytochrome. The spectra show that protonated carboxyl groups are influenced. The small amplitudes in the difference spectra exclude major changes of protein secondary structure.

Fourier Analysis↗
PubMed1990

Modified reaction centers from Rhodobacter sphaeroides R26. 2: Bacteriochlorophylls with modified C-3 substituents at sites BA and BB.

Monomeric bacteriochlorophylls BA and BB in photosynthetic reaction centers from Rhodobacter sphaeroides R26 were exchanged with (13(2)-hydroxy-)bacteriochlorophylls containing a 3-vinyl- or 3-(alpha-hydroxyethyl)-substituent instead of the 3-acetyl group. The corresponding binding sites must be tolerant to the introduction of the polar residue at C-13(2) and modifications of the 3-acetyl group. According to HPLC analysis, the exchange with both pigments amounts to less than or equal to 50% of the total BChl contained in the complex, corresponding to less than or equal to 100% of the monomeric BChl alpha BA,B. The absorption spectra show significant changes in the QX and QY-region of the monomeric bacteriochlorophylls. By contrast, the absorption of the primary donor (P870) and reversible photobleaching is retained. The circular dichroism is also unchanged in the 870 nm region. The positive cd band located at around 800 nm in native reaction centers, shifts with the (blue-shifted) QY absorption(s) of BA and/or BB, whereas the position of the negative one remains nearly unaffected. The data indicate that the latter is the upper excitonic band of the primary donor, and that there is little interaction of the monomeric BA/BB with the primary donor.

Bacteriochlorophylls↗
PubMed1986

Reconstitution of the purified alpha-latrotoxin receptor in liposomes and planar lipid membranes. Clues to the mechanism of toxin action.

The receptor of alpha-latrotoxin (the major toxin of the black widow spider venom), purified from bovine synaptosomal membranes, was reconstituted into small unilamellar liposomes. These (but not control) liposomes exhibited high-affinity, specific binding of [125I]alpha-latrotoxin. In the receptor-bearing liposomes alpha-latrotoxin induced depolarization and stimulated 45Ca efflux. These responses to alpha-latrotoxin, that were observed only in the presence of external divalent cations, resembled those previously demonstrated in mammalian brain synaptosomes. The alpha-latrotoxin-activated ion fluxes are therefore, at least in part, the result of the direct interaction of the toxin with its receptor. When control and receptor-bearing liposomes were pre-incubated with alpha-latrotoxin and then added to a solution bathing a planar lipid bilayer membrane, single channel cationic conductances were observed. In the presence of the receptor, the conductances induced by alpha-latrotoxin were markedly different from those observed without the receptor, but not identical to those observed without the receptor, but not identical to those recently characterized by patch clamping in the cells of a line (PC12) sensitive to alpha-latrotoxin. These results demonstrate that the reconstituted receptor is functional, and suggest that the cationic channel activated by the toxin-receptor interaction is modulated by additional component(s) in the membrane of synapses and cells.

Animals↗
PubMed1985

Purification of the putative alpha-latrotoxin receptor from bovine synaptosomal membranes in an active binding form.

alpha-Latrotoxin (alpha-LTx, apparent mol. wt. 130 000) is a presynaptically active neurotoxin purified from the venom of the black widow spider that causes massive exocytotic release of neurotransmitters, presumably via binding to presynaptic membrane protein(s). Solubilization and purification experiments were undertaken to identify and characterize this membrane component. An immunoaffinity matrix was prepared by sequentially binding anti-alpha-LTx antibodies and alpha-LTx to Protein A-Sepharose CL-4B. Beads were irreversibly cross-linked with dimethyl pimelimidate. These beads were capable of extracting alpha-LTx binding activity from Triton X-100 solubilized bovine synaptosomal membranes. Following extensive washing, bound material was eluted with 6 M urea. Analysis of silver stained and radiolabel-containing gels revealed one major band (apparent mol. wt. 200 000) under non-reducing conditions and two major bands (apparent mol. wts. 66 000 and 54 000) under reducing conditions. The purified material was still capable of specifically binding alpha-LTx as determined by solid phase assays on microtiter plates. The affinity for alpha-LTx of the purified preparation was similar to that of the native membrane (KA approximately 10(10) M). It is concluded that a putative alpha-LTx receptor protein can be purified from synaptosomal membranes using an immunoaffinity matrix in a form that retains its defined biological property (alpha-LTx binding).

Animals↗
PubMed1984

Alpha latrotoxin of black widow spider venom: an interesting neurotoxin and a tool for investigating the process of neurotransmitter release.

Alpha latrotoxin, purified from the venom of the black widow spider, is a high Mr (130000) protein devoid of detectable enzymatic activity. When applied to vertebrate nerve terminals (of the central as well as peripheral nervous systems) the toxin elicits massive release of neurotransmitters by stimulating the fusion of synaptic vesicles with the presynaptic membrane (exocytosis). Among non-neuronal systems, only the neurosecretory cell line PC12 is sensitive to alpha latrotoxin; all others investigated so far are insensitive. In order to act, alpha latrotoxin requires the presence of divalent cations in the medium. Ca2+ can be substituted by other divalent cations as Sr2+, Ba2+, Mn2+, Mg2+. However, with the last two the catecholamine release response is reduced in PC12 cells and synaptosomes. A specific, high affinity receptor of alpha latrotoxin exists in preparation sensitive to the toxin. This receptor has been purified and found to be a high Mr, integral membrane protein. In the frog neuromuscular junction the receptor is localized exclusively in the presynaptic membrane. Binding of alpha latrotoxin to the receptor in a Ca2+-containing incubation medium induces membrane depolarization (insensitive to tetrodotoxin), stimulation of Ca2+ influx (insensitive to verapamil) with consequent increase in the cytoplasmic free Ca2+ concentration and stimulation of phosphoinositide breakdown. In Ca2+ free medium depolarization is maintained, but free Ca2+ concentration does not rise after toxin application. In conclusion, alpha latrotoxin seems to act through a dual mechanism. The Ca2+-independent part of this mechanism may be mediated by the activation of protein kinase C, triggered by phosphoinositide metabolism. The relevance of these findings for presynaptic physiology is discussed.

Animals↗
PubMed1983

Solubilization and partial characterization of rat epididymal delta 4-steroid 5 alpha-reductase (cholestenone 5 alpha-reductase).

Epididymal delta 4-steroid 5 alpha-reductase (cholestenone 5 alpha-reductase), the enzyme that catalyses the conversion of testosterone into the biologically active metabolite dihydrotestosterone (17 beta-hydroxy-5 alpha-androstan-3-one), is a membrane-bound enzyme found in both nuclear and microsomal subcellular fractions. In order to characterize epididymal delta 4-steroid 5 alpha-reductase, it was first necessary to solubilize the enzymic activity. Of the various treatments tested, a combination of 0.5% (w/v) Lubrol WX, 0.1 M-sodium citrate and 0.1 M-KCl maintained enzymic activity at control values and solubilized 66% of total epididymal delta 4-steroid 5 alpha-reductase activity in an active and stable form. The sedimentation coefficient of solubilized delta 4-steroid 5 alpha-reductase, as determined in continuous sucrose density gradients, was greater for the microsomal than for the nuclear enzyme (11.6S compared with 10.1S). Although the apparent Km values of the enzyme for testosterone were similar in nuclear and microsomal subcellular fractions (range 1.75 x 10(-7) - 4.52 x 10(-7)M), the apparent Km of the enzyme for NADPH was about 30-fold greater for the microsomal enzyme than for the nuclear enzyme. The apparent Km of the enzyme for either substrate was not significantly altered after solubilization. The relative capacity of steroids to inhibit the enzymic activity, the pH optima and the effects of Ca2+ and Mg2+ were similar for membrane-bound and solubilized delta 4-steroid 5 alpha-reductase in both the nuclear and the microsomal fractions. The results reported demonstrate that epididymal delta 4-steroid 5 alpha-reductase can be solubilized in an active and stable form with no significant changes in the kinetic characteristics of the enzyme after solubilization; furthermore, kinetic and molecular-size differences observed for the nuclear and the microsomal forms of the enzyme suggest that there may exist at least two forms of epididymal delta 4-steroid 5 alpha-reductase.

Animals↗
PubMed1983

Subcellular distribution of steroid delta 4-5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase in the rat epididymis during sexual maturation.

The curve of the specific activity of rat epididymal nuclear delta 4-5 alpha-reductase is bell shaped as a function of age, whereas that of cytoplasmic 3 alpha-hydroxysteroid dehydrogenase does not change significantly with age. The present study examines the subcellular distribution of delta 4-5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase in the caput-corpus and cauda epididymidis during development. A 5-step discontinuous sucrose gradient was developed for fractionation of epididymal homogenates. By using enzyme markers specific for different subcellular organelles, the five different subcellular fractions obtained were shown to be of cytoplasmic, microsomal, mitochondrial, nuclear and spermatozoal origin. 3 alpha-Hydroxysteroid dehydrogenase activity was associated only with the cytoplasmic fraction. The activity of the enzyme did not change significantly with age in either the caput-corpus or cauda epididymidis. delta 4-5 alpha-Reductase activity was found in fractions containing microsomal and nuclear markers. delta 4-5 alpha-Reductase activity in the nuclear fraction of the caput-corpus epididymidis was evident in the youngest age group (Day 25), increased 4-fold and peaked in the next age group (Day 35), and declined with each successive age group: Day 45 (60% of maximum), Day 60 (20% of maximum), Day 75 (15% of maximum) and Day 105 (10% of maximum). In contrast, microsomal delta 4-5 alpha-reductase activity increased successively from Day 25 to Day 105; enzyme activity doubled between these two ages. The ratio of nuclear to microsomal delta 4-5 alpha-reductase activity from the caput-corpus epididymidis thus changed markedly with age: Day 25:1.32; Day 35:3.76; Day 45:2.44; Day 60:1.03; Day 75:0.41; and Day 105:0.21. In the cauda epididymidis nuclear delta 4-5 alpha-reductase activity was only evident at Day 35 and Day 45; in microsomal fractions, activity was first found at Day 35 and did not subsequently change with age. These results demonstrate that: 1) epididymal 3 alpha-hydroxysteroid dehydrogenase activity is found only in the cytoplasmic fraction; 2) delta 4-5 alpha-reductase activity is found in nuclear and microsomal fractions; and 3) the subcellular distribution of delta 4-5 alpha-reductase activity changes markedly with age and epididymal section, suggesting differential regulation of nuclear and microsomal delta 4-5 alpha-reductase activities.

3-Hydroxysteroid Dehydrogenases↗
PubMed1982

Recombination dynamics in bacterial photosynthetic reaction centers.

The time dependence of magnetic field effects on light absorption by triplet-state and radical ions in quinone-depleted reaction centers of Rhodopseudomonas sphaeroides strain R-26 has been investigated. Measurements on the time scale of the hyperfine interaction in the radical pair [(BChl)2+. ...BPh-.)] provided kinetic data characterizing the recombination process. The results have been interpreted in terms of a recently proposed model that assumes an intermediate electron acceptor (close site) between the bacteriochlorophyll "special pair" (BChl)2 and the bacteriopheophytin BPh (distant site). Recombination is assumed to proceed through this intermediate acceptor. The experiments led to effective recombination rates for the singlet and triplet channel: k(Seff) = 3.9 . 107 s-1 and k(Teff) = 7.4 . 10(8) s-1. These correspond to recombination rates ks = 1 . 10(1) s-1 and kT = 7.1 . 10(11) s-1 in the close configuration. The upper bound of the effective spin dephasing rate k2eff approximately equal to 1 . 10(9) s-1 is identical with the rate of the electron hopping between the distant site of zero spin exchange interaction and the close site of large interaction. Interpretation of data for the case of direct recombination yields the recombination rates, spin dephasing rate, and exchange interaction in a straightforward way.

Bacterial Proteins↗
PubMed1980

Steroid delta 4-5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase in the rat epididymis during development.

delta 4-5 alpha-Reductase activity is apparently regulated by a testicular factor(s) secreted directly into the epididymis, whereas 3 alpha-hydroxysteroid dehydrogenase activity, in this tissue, appears to reflect circulating androgen levels. To test whether the factor(s) regulating delta 4-5 alpha-reductase activity is directly associated with spermatozoa, a developmental study was undertaken to temporally correlate various parameters of the male reproductive tract with enzymatic activities. delta 4-5 alpha-Reductase activity is first detectable at 21 days of age. Activity increases until day 77, after which time enzymatic activity decreases by more than 60%, reaching steady adult values at 105 days. 3 alpha-Hydroxysteroid dehydrogenase activity is detectable as early as 7 days. Levels of this enzyme increase until day 63, after which time constant adult values are maintained until at least 1 yr. Spermatids and/or spermatozoa are first seen in the testes at 42 days, and plateau levels are reached by day 77. Spermatozoa are first seen in the epididymis at 49 days and reach maximal values by 91 days; no significant change occurs thereafter (until 365 days). Increases in seminal vesicle and ventral prostate weights are of a sigmoidal type, paralleling increases in plasma androgens, with the greatest rate of rise between days 35--63. This sigmoidal type of increase in tissue weights and plasma androgens is similar to that seen for epididymal 3 alpha-hydroxysteroid dehydrogenase but markedly different from that found for delta 4-5 alpha-reductase. The importance of delta 4-5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase activities in the epididymis before the entry of spermatozoa and the decline in delta 4-5 alpha-reductase activity with age is discussed.

3-Hydroxysteroid Dehydrogenases↗
PubMed1979

Studies on plant bile pigments, VII. Preparation and characterization of phycobiliproteins with chromophores chemically modified by reduction.

The reversible denaturation and reduction with dithionite has been studied for the phycobiliproteins, C-phycocyanin (1) and allophycocyanin (2) from Spirulina platensis, and C-phycoerythrin (4) from Fremyella diplosiphon (both cyanobacteria). By treatment with sodium dithionite, the chromophores are selectively reduced at the central (C-10) methine bridge, producing pigments with bilirubinoid (lambda max = 418 nm from 1 and 2), and vinylpyrroloc (lambda max= 300 nm from 4) chromophores. The extent of reduction is dependent on the state of the protein. The chromophores of denatured biliproteins are completely reduced at 0.5 mM dithionite. In the native pigments, dithionite concentrations up to 0.5 mM lead only to partial reduction, thus forming products containing both reduced and oxidized chromophores (e.g. "phycocyanorubins" from 1 and 2). The reduction is non-statistical with respect to the different chromophores present in 1 and 4, the chromophores absorbing at shorter wavelengths being preferentially reduced. Renaturation of the proteins containing reduced chromophores is accompanied by their reoxidation. This oxidation is complete in the absence of dithionite or at concentrations up to 0.5 mM. At higher dithionite concentrations, the reoxidation is incomplete, and the products are spectroscopically identical to those obtained by reduction of the native pigments at similar concentrations of reductant. The results are interpreted by a model in which the protein is "transparent" to the reducing agent, dithionite. The difference in the extent of reduction of the native and denatured pigments can only be due to thermodynamic (viz. stability) differences in the susceptibility of the chromophores to reduction. Specifically, the (extended) chromophore present in the native pigment is much more difficult to reduce than the chromophore (present in a cyclic conformation) in the denatured pigment. The energetics of the process of refolding both the protein and the chromophores are discussed.

Apoproteins↗
PubMed1979

[Reaction of articular cartilage to subchondral defect filling with autologous cancelous bone, Kiel's bone chips and bone cement].

Equally sized subchondral osseous defects were produced in 30 adult rabbits. The defects were filled with autologous cancellous bone, bone cement, or macerated heterologous cancellous bone. Twelve weeks later those filled with autologous cancellous bone showed consolidation with preservation of the subchondral border line. There were no degenerative changes of the joint's cartilage. Filling with bone cement or heterologous cancellous bone, on the other hand, led to destruction of the joint's cartilage. The defects treated with heterologous cancellous bone had not reached osseous consolidation at that time. These results suggest that effective treatment of subchondral osseous defects can only be achieved by filling with autologous cancellous bone.

Animals↗
PubMed1977

On the classification of penis carcinoma and its 10-year survival.

With respect to the primary tumor there is no difference between the proposal of the UICC and the Heidelberg version for TNM classification of the penis carcinoma. Clinically the Heidelberg scheme seems more practical, but there were no statistical differences between them. With respect to the prognosis for the patient, the size and localization of the primary tumor are of secondary importance. What is important is the degree of tumor spreading in the lymph system. From this point of view, one needs only to differentiate between T1 (tumor restricted to the penis) and T2 (tumor extending the bounds of the penis). On the other hand, size, localization, and degree of infiltration of penis carcinoma do have different therapeutic consequences, so from this point of view the differentiation of the primary tumor from T1 up to T4 should be retained. With respect to the classification of the state of the corresponding lymph system it is our opinion that the UICC proposal is too differentiated and has little meaning. In its stead, the Heidelberg scheme is clear and simple. Any examiner can complete it. With the help of life tables extending beyond 10 years after diagnosis we were able to determine that 5 years is not a sufficiently long time to clsoe a case of penis cancer. Even with proper treatment, the patient may suffer up to 10 years or more from the disease. In patients aged between 50 and 59 years of age the cancer seems to grow faster; in spite of proper and intensive treatment those patients had a clearly limited life expectancy. In patients aged 60-69 and more so in those between 70 and 79 years of age the tumor seemed to grow slowly and often had no effect on the survival rate.

Follow-Up Studies↗
PubMed1977

Studies on plant bile pigments, II[1]. Chemical and photochemical oxygenation of a phytochrome Pr chromophore model pigment to purpurins.

The chemical and photochemical oxygenation of 2,3-dihydrooctaethyl-1,19(21,24H)-bilindione (1), as a model for the chromophores of both phytochrome Pr and phycocyanin, has been studied in neutral and alkaline solution, and in the presence of zinc ions. By comparison with octaethyl-1,19(21,24H)-bilindione (5), the influence of ring A hydrogenation on the reactivity of bilins has been assessed. In the dark, 1 is attacked selectively and rapidly at C-5 yielding "purpurins", while 5 reacts slowly, and is attacked predominantly at C-10. Photooxidation of 5 yields the tripyrrinic "purpurin" 7 only. Photoreactivity of 1 is considerably enhanced, yielding "purpurins" and "violins" rapidly. In spite of UV-vis and mass spectroscopic similarities, the "purpurin" 7 differs from the "purpurins" 6a,b by the loss of ring A. The facile cleavage at the C-5 methine bridge and the spectroscopic properties of "purpurins" are discussed.

Models, Chemical↗