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A Schnegg

Publications and source records attributed to A Schnegg.

At least 19 recordsLinked to original sources
PubMed2005

Combining high-field EPR with site-directed spin labeling reveals unique information on proteins in action.

In the last decade, joint efforts of biologists, chemists and physicists have helped in understanding the dominant factors determining specificity and directionality of transmembrane transfer processes in proteins. In this endeavor, electron paramagnetic resonance (EPR) spectroscopy has played an important role. Characteristic examples of such determining factors are hydrogen-bonding patterns and polarity effects of the microenvironment of protein sites involved in the transfer process. These factors may undergo characteristic changes during the reaction and, thereby, control the efficiency of biological processes, e.g. light-induced electron and proton transfer across photosynthetic membranes or ion-channel formation of bacterial toxins. In case the transfer process does not involve stable or transient paramagnetic species or states, site-directed spin labeling with suitable nitroxide radicals still allows EPR techniques to be used for studying structure and conformational dynamics of the proteins in action. By combining site-directed spin labeling with high-field/high-frequency EPR, unique information on the proteins is revealed, which is complementary to that of X-ray crystallography, solid-state NMR, FRET, fast infrared and optical spectroscopic techniques. The main object of this publication is twofold: (i) to review our recent spin-label high-field EPR work on the bacteriorhodopsin light-driven proton pump from Halobacterium salinarium and the Colicin A ion-channel forming bacterial toxin produced in Escherichia coli, (ii) to report on novel high-field EPR experiments for probing site-specific pK(a) values in protein systems by means of pH-sensitive nitroxide spin labels. Taking advantage of the improved spectral and temporal resolution of high-field EPR at 95 GHz/3.4 T and 360 GHz/12.9 T, as compared to conventional X-band EPR (9.5 GHz/0.34 T), detailed information on the transient intermediates of the proteins in biological action is obtained. These intermediates can be observed and characterized while staying in their working states on biologically relevant timescales. The paper concludes with an outlook of ongoing high-field EPR experiments on site-specific protein mutants in our laboratories at FU Berlin and Osnabrück.

Bacteriorhodopsins↗
PubMed2002

Orientation selection in photosynthetic PS I multilayers: structural investigation of the charge separated state P(700)(+z.rad;)A(1)(-z.rad;) by high-field/high-frequency time-resolved EPR at 3.4 T/95 GHz.

The radical-pair state of the primary electron donor and the secondary electron acceptor (P(700)(+z.rad;)A(1)(-z.rad;)) of the photosynthetic reaction center (RC) photosystem I (PS I) of Synechocystis PCC 6803 was studied by time-resolved electron paramagnetic resonance (TREPR) at high field/high frequency (3.4 T/95 GHz) using orientation selection in multilayers. The goal of the present article is to work out the basis for future studies, in which the improved resolution of such multilayers may be used to detect mutation-induced structural changes of PS I in membrane preparations. This approach is particularly interesting for systems that cannot be prepared as single crystals. However, in order to use such multilayers for structural investigations of protein complexes, it is necessary to know their orientation distribution. PS I was chosen as a test example because the wild type was recently crystallized and its X-ray structure determined to 2.5 A resolution [Nature 411 (2001) 909]. On the basis of our experimental results we determined the orientation distribution. Furthermore, a simulation model for the general case in which the orientation distribution is not axially symmetric about the C(2) symmetry axis of the RC is developed and discussed. Spectra simulations show that changes in the TREPR spectra of PS I are much more significant for these oriented multilayers than for disordered samples. In this way the use of oriented multilayers, in conjunction with multifrequency TREPR measurements on oriented as well as on disordered samples, is a promising approach for studies of structural changes of PS I systems that are induced by point mutations.

Anisotropy↗
PubMed1982

[Contents and distribution of Fe, Cu, Zn, Ni, and Mn in fetuses, amniotic fluid, placenta, and uterus of rats].

Fetuses, amniotic fluid, placenta, and uterus were taken from five gravid rats shortly prior to delivery, and the contents of Fe, Cu, Zn, Ni, and Mn were analyzed. Fe, Cu, Zn, and Mn exhibited a similar concentration in dry matter (DM) in all tested reproductive organs, whereby Fe-contents were five to ten times higher than Zn-contents and those five to ten times higher than Cu-contents, which amounted to 10-20 ppm. The Mn-contents range about a factor of ten below. Ni-concentration in DM of fetuses, placenta and uterus is below 1 ppm, whereas in contrast to this, Ni-concentration of 14 ppm in DM of amniotic fluid is 34 times higher than in fetuses and placenta. Uterus contained twice as much Ni as fetuses. Concerning the total content of the individual trace elements, Ni reacts also different as compared to Fe, Cu, Zn, and Mn. Its amniotic content exceeds the fetal content by 40%. Total excretion of Fe, Cu, Zn, Mn, and also DM is distributed differently as compared to Ni. Fetuses contain 60%-70% of these trace elements, placenta 15%-25%, uterus 6%-16%, and amniotic fluid only 1%-2%. Ni, however, is excreted mostly via amniotic fluid by about 35% of total excretion and only by about 25% via fetuses. These findings, concerning Ni, are discussed in detail.

Amniotic Fluid↗
PubMed1981

[Alpha amylase and dehydrogenase activity in suboptimal Ni intake].

Supplementary to studies on the activity of various enzymes during Ni deficiency, the present work was done to determine their response to suboptimal Ni supply. Live weight gain of rats was not affected by 60 versus 150 ppb Ni in the diet. The activity of alpha-amylase, however, was reduced by 43% in the case of 60 ppb dietary Ni and in relation to the change in this enzyme the activity of glucose-6-phosphate dehydrogenase by 56% and of the lactate dehydrogenase by 27%. These dehydrogenases responded with increased activities to the slight raise in Ni supply with the diet containing 150 ppb Ni as compared to the group given 60 ppb dietary Ni. Overall, it may be inferred that growth is not affected unless dietary Ni supply is below 50 ppb and that dietary Ni contents of 60 and 150 ppb must be regarded as suboptimal supply levels because of the diminished activity of various enzymes.

Amylases↗
PubMed1980

[Effects of iron supply and lactation on iron availability in intermediate metabolism].

The availability of iron in metabolism was determined in dependence on the performance after lactation had finished and on the level of Fe-supply of a total of 56 rats. The availability of iron of those animals which had reared young was, according to the increased requirement, high and decreased from 87 to 54% after increased doses of iron. The values of full-grown control animals were considerably lower and had a falling tendency from 52 to 36% after an increasing supply with iron. Because of the reduced utilization of iron after increased supply the gross requirement must be increased over-proportionally when the net requirement rises.

Animals↗
PubMed1980

[Deficient nickel supply and the content of calcium, magnesium and phosphorus inthe bone of growing rats].

Based upon studies on Ni deficiency with marked changes in intermediary metabolism, the recent investigation examined the extent to which deficient Ni supply affects the content of calcium, magnesium and phosphorus in rat femurs. In Ni deficiency the content of calcium and phosphorus was reduced, in the case of calcium even more so than accounted for by the decrease in bone weight. The result was Ca : P ratio of 1.8 : 1 in Ni deficiency compared with 2.0 : 1 in control animals. In the case of magnesium, however, the Mg concentration was increased by 45% in the bone fresh matter of the deficient animals. The reduced Ca retention in the bone is accordingly contrasted by an enhanced deposition of magnesium.

Animals↗
PubMed1979

[Activity of proteases, leucine arylamidase and alpha-amylase in pancreatic tissue during nickel deficiency].

In studies on the essentiality of nickel, important differences of enzyme activities and also of substrates were established. The results of the present paper show that these changes cannot be explained by a lowered reduction of dietary proteins, since the activity of the proteases rather increased during Ni deficiency. However, the digestion of the starch by alpha-amylase, being 57% lower, could have been partially responsible for the large differences in the activities of the hepatic enzymes and in the concentrations of the hepatic metabolites and also in the weight gains.

Aminopeptidases↗
PubMed1977

A comparative view on trace elements and growth.

The term 'essentiality' of trace elements is interpreted. The major human diseases due to trace element deficience (Fe, Cu, Zn, Cr) are briefly considered. In growing animals the first clinical deficiency symptom most often is a growth retardation. In order to diagnose a deficient situation before the manifestation of clinical symptoms, model studies with growing animals are presented to show criteria that respond sensitively even to suboptimum intake of trace elements (Zn, Cu, Fe, Ni). Activity measurements of enzymes and hormones are found suitable. During the phase of reproduction, which is closely associated with growth, the trace element concentration in milk may provide an additional diagnostic means. In conclusion, the problems of diagnosing the supply status are discussed. A possibility for determination of the trace element requirement is indicated.

Animals↗
PubMed1977

[Alkaline and acid phosphatase activity in the liver and serum during Ni versus Fe deficiency].

In previous studies on the essentiality of nickel, a reduced iron absorption causing anemia was observed. Since Ni deficiency also affects Zn metabolism, the different phosphatase activities were determined. Ni deficiency, however, resulted in an increased activity of the alkaline phosphatase in liver. On the other hand, the activity of the alkaline phosphatase was deduced by 59% during Fe deficiency. Similarly, the alkaline and acid phosphatases in serum were reduced during Fe deficiency. Consequently, determination of the activity of the alkaline phosphatase in serum, besides that of various liver enzymes, is suited well to differentiate between Fe and Ni deficiency.

Acid Phosphatase↗
PubMed1976

Malate dehydrogenase and glucose-6-phosphate dehydrogenase activity in livers of Ni-deficient rats.

In experiments using rats it was shown that inadequate dietary supply of Ni reduces growth and lowers the erythrocyte count, hematocrit and hemoglobin level in blood, that the Ni supply affects the trace element content of iron, copper and zinc in various body organs, and that the absorption of iron is greatly impaired by Ni deficiency. For further biochemical criteria on the essentiality of nickel, the activities of two dehydrogenases, malate dehydrogenase and glucose-6-phosphate dehydrogenase, were measured in liver homogenates from two generations of rats at 30 and 50 days of age. In the 30-day-old rats of both the F1 and F2 generation, the activity of the malate dehydrogenase fell to about two-thirds the level of control animals. In the liver of the 50-day-old rats the activity of this enzyme was about the same in deficient animals as in the controls. The activity of glucose-6-phosphate dehydrogenase of Ni-deficient rats was reduced by 85% in the F1 generation and by 56% in the F2 generation at 30 days of age as compared with control levels. In 50-day-old rats the activity had fallen to half the level of control animals at 30 days of age. At the age of 50 days, there was no significant difference between the deficient and the control groups of either generation.

Animals↗
PubMed1976

[Nickel content in the milk of lactating rats under intake of various amounts of nickel].

Model experiments were carried out with rats showing that the average Ni concentrations in the milk of the experimental animals receiving a Ni deficient diet (40 ppb of dietary Ni), relative to those of the controls (20 ppm), declined from 1088 ng/g to 726 ng/g (33%). This produced a Ni deficiency in the youngs of the rats resulting in retarded growth, reduced Fe absorption and a decline in enzymatic activity. An increase in the Ni content of the milk from both the experimental animals and the controls was observed during lactation. In the Ni deficient group this upward trend was longer noticeable from about the middle of the lactation period onwards. Animals in the Ni deficient group excreted about three times as much Ni through the milk as was ingested with the food. Because of the wide range of deviations of the Ni content in the different animals the Ni content of the milk cannot be used, under practical conditions, as an index of a state of Ni deficiency.

Animal Feed↗
PubMed1976

[Interaction of nickel with iron, copper and zinc].

Studies were carried out investigating the role of nickel as an essential element in the growth of rats. Reduced levels of iron, copper and zinc were found in the liver, spleen and kidneys during Ni deficiency. These findings could be reproduced in 2 generations of 30-day and 50-day-old rats. Reduced rates of Fe storage during Ni deficiency were, in some cases, even noted of the Fe supply was raised to a level of as high as 100 mg Fe per kg of the diet. This accounted for the diminished haemoglobin values, the reduced erythrocyte count and reduced hematocrite found under conditions of Ni deficiency.

Animals↗
PubMed1976

[Absorption and metabolic efficiency of iron in nickel deficiency].

Absorption and Metabolic Efficiency of Iron During Ni Deficiency. Ni deficiency leads to reduced iron contents in organs and to greatly reduced Hb levels and erythrocyte counts. Using models it was studied whether this Ni-dependent Fe anemia can be attributed to an impaired absorption of iron or to its metabolic efficiency. An experiment with seven 30-day-old rats from each of two generations were used for this. In Ni deficiency (0.015 ppm dietary nickel) iron absorption was clearly impaired at both 50 ppm and 100 ppm iron in the diet. Compared to the groups given 20 ppm nickel, the amount of iron absorbed fell two-thirds and one-third, respectively. By comparison, the influence on the metabolic efficiency of the iron was relatively small; at high iron supply, however, it was reduced by 8% in the Ni-deficient animals. Therefore, the reduced levels of hemoglobin, erythrocytes and hematocrit must essentially be caused by the impared absorption.

Animals↗