Biomedical subjects

H Senger

Publications and source records attributed to H Senger.

At least 19 recordsLinked to original sources

PubMed2001

Electron pathways involved in H(2)-metabolism in the green alga Scenedesmus obliquus.

The green alga Scenedesmus obliquus is capable of both uptake and production of H(2) after anaerobic adaptation (photoreduction of CO(2) or photohydrogen production). The essential enzyme for H(2)-metabolism is a NiFe-hydrogenase with a [2Fe-2S]-ferredoxin as its natural redox partner. Western blot analysis showed that the hydrogenase is constitutively expressed. The K(m) values were 79.5 microM and 12.5 microM, determined with ferredoxin and H(2), respectively, as electron donor for the hydrogenase. In vitro, NADP(+) was reduced by H(2) in the presence of the hydrogenase, the ferredoxin and a ferredoxin-NADP reductase. From these results and considerations on the stoichiometry we propose that this light-independent electron transfer is part of the photoreduction of CO(2) in vivo. For ATP synthesis, necessary for the photoreduction of CO(2), light-dependent cyclic electron transfer around Photosystem (PS) I accompanies this 'dark reaction'. PS II fluorescence data suggest that (a) in S. obliquus H(2)-reduction might function as the anaerobic counterpart of the O(2)-dependent Mehler reaction, and (b) the presence of either a ferredoxin quinone-reductase or NAD(P)-dehydrogenase (complex I) in S. obliquus chloroplasts.

Anaerobiosis↗

PubMed2001

Molecular evidence for a Fe-hydrogenase in the green alga Scenedesmus obliquus.

Fe-hydrogenase-specific degenerate primers were used in polymerase chain reactions with single-stranded Scenedesmus obliquus cDNA as template. A resulting 435-bp fragment was used to screen a cDNA library from S. obliquus. A 1.6-kb cDNA clone, containing the 3'-end of an open reading frame, was obtained. Its deduced amino acid sequence contains the conserved H-cluster motives unique for Fe-hydrogenases. Any other FeS-clusters seem to be absent. Phylogenetically, the enzyme is closely related to the Trichomonas vaginalis Fe-hydrogenase. Northern blot analysis shows that the Fe-hydrogenase is constitutively expressed in S. obliquus. Southern blot analysis of plastidic, mitochondrial, and nuclear DNA reveals that the enzyme is a single-copy gene encoded in the nucleus. Effects of transcriptional and translational inhibitors on H2-metabolism reveal the involvement of a chloroplast-encoded protein.

Amino Acid Sequence↗

PubMed1999

Redox control of hydrogenase activity in the green alga Scenedesmus obliquus by thioredoxin and other thiols.

The activity of the NiFe-hydrogenase from the green alga Scenedesmus obliquus is inhibited by both algal thioredoxins f and I+II, and by Escherichia coli thioredoxin. The strongest inhibition was observed with homologous chloroplastic thioredoxin f (I50 = 21 nM) and E. coli thioredoxin (I50 = 83 nM). For the homologous cytoplasmic thioredoxins I+II an I50 of 667 nM was determined. Glutathione shows a similar but much less pronounced inhibitory effect whereas dithiothreitol had no effect. In addition to glucose-6-phosphate dehydrogenase, NiFe-hydrogenase is only the second enzyme known to be inhibited by reduced thioredoxin.

Chlorophyta↗

PubMed1997

Light-harvesting in Acaryochloris marina--spectroscopic characterization of a chlorophyll d-dominated photosynthetic antenna system.

Oxygenic photosynthesis of the prokaryote Acaryochloris marina involves chlorophyll d (Chl d) as the major pigment [Miyashita et al. (1996) Nature 383, 402]. Four spectral forms of Chl d (peak wavelengths: 694, 714, 726 and 740 nm) are resolvable by low-temperature absorption spectroscopy on intact cells. Based on fluorescence spectra (at 290 K and 77 K) and on analysis of fluorescence induction curves we conclude: (1) excitation energy is efficiently transferred between the various spectral forms of Chl d and the PS II reaction center; (2) Chl d serves as a light-harvesting pigment for both, Photosystem II (PS II) and PS I; (3) excitation energy transfer between PS II units occurs.

Chlorophyll↗

PubMed1997

Isolation and characterization of biliprotein aggregates from Acaryochloris marina, a Prochloron-like prokaryote containing mainly chlorophyll d.

Phycobiliprotein aggregates were isolated from the prokaryote Acaryochloris marina, containing chlorophyll d as major pigment. In the electron microscope the biliprotein aggregates appear as rod-shaped structures of 26.0 x 11.3 nm, composed of four ring-shaped subunits 5.8 nm thick and 11.7 nm in diameter. Spectral data indicate that the aggregates contain two types of biliproteins: phycocyanin and an allophycocyanin-type pigment, with very efficient energy transfer from the phycocyanin- to allophycocyanin-type constituent. The chromophore-binding polypeptides of the pigments have apparent molecular masses of 16.2 and 17.4 kDa. They crossreact with antibodies against phycocyanin and allophycocyanin from a red alga.

Bacterial Proteins↗

PubMed1995

Complete separation of the beta,epsilon- and beta,beta-carotenoid biosynthetic pathways by a unique mutation of the lycopene cyclase in the green alga, Scenedesmus obliquus.

The mutant, C-2A'-34, lacks the beta, epsilon-carotenoids, alpha-carotene, lutein and loroxanthin. When grown under heterotrophic or mixotropic conditions this strain develops significantly higher levels of beta-carotene and violaxanthin than does the original developmental mutant of Scenedesmus, C-2A'. The decrease in chlorophyll a and chlorophyll b observed in C-2A'-34 is accompanied by the near absence of the LHC. The light intensity dependence of greening of this strain is comparable to that of C-2A'; the loss of the beta,epsilon-carotenoids and modification of the pool of beta,beta-carotenoids neither prevent the proximal pigment-protein complexes of photosystems I and II from developing nor cause any short term photosensitivity. The increase in the beta,beta-carotenoids in C-2A'-34 apparently compensates for the loss of the beta,epsilon-carotenoids required in formation of the proximal and distal antennae systems but not in the LHCs.

Carotenoids↗

PubMed1994

Isolation and characterization of phototropism mutants of Phycomyces insensitive to ultraviolet light.

Phototropism mutants of the zygomycete fungus Phycomyces blakesleeanus were isolated on the basis of their loss of responsivity to UV light. Four of these mutants had retained a partial sensitivity to near-UV and to blue light. Gravitropism and the avoidance response were unaffected in these mutants. One mutant, A909, had lost most of its sensitivity to near-UV and blue light while the sensitivity to far-UV light was only slightly affected. Additionally, the gravitropic and the avoidance responses were significantly reduced in A909. A complementation analysis of the five strains of Phycomyces with known phototropism mutants indicated that strains A896, A897, and A898 were defective in the madA gene, and that A905 was affected in the madC gene. In strain A909 the input, as well as the output, of the transduction chain is affected.

Carotenoids↗

PubMed1993

Characterization and purification of a hydrogenase from the eukaryotic green alga Scenedesmus obliquus.

Several catalytic properties of the hydrogenase from Scenedesmus obliquus have been examined to optimize the purification conditions. The Km-value for H2-evolution in the presence of the most effective electron mediator methylviologen is 0.66 mM. The pH-optimum is 6.3, the temperature-optimum is 50 degrees C and the energy of activation is 38.4 +/- 2 kJ.mol-1. The soluble hydrogenase from the green alga, Scenedesmus obliquus, was purified 1290-fold to homogeneity. The enzyme consists of two subunits with molecular masses of 55 kDa and 36 kDa. The molecular weight of the native enzyme, determined by gel filtration, is 150 +/- 5 kDa.

Chlorophyta↗

PubMed1993

Nitrogen and fat balances in very low birth weight infants fed human milk fortified with human milk or bovine milk protein.

The study was designed to compare two different human milk fortifiers in a group of very low birth weight (VLBW) infants by analysing nitrogen and fat balances, serum concentrations of alpha-amino-nitrogen, urea, and prealbumin as well as growth rates when human milk enriched with one of the two studied fortifiers was fed to the infants. Fortifier A contained different bovine proteins, peptides and amino acids and had an amino acid composition comparable to that of the nutritional available proteins in human milk, with carbohydrates, and minerals. Fortifier B was composed of freeze-dried skimmed human milk and minerals to achieve a similar macronutrient composition in both fortifiers. Eleven infants were fed with human milk enriched with fortifier A and 13 with fortifier B. After a 10-day equilibration period, a 3-day metabolic balance was performed. On the 14th day of the study blood was obtained preprandially for serum analysis and growth rates were estimated. The nitrogen absorption rate (93.8% vs 93.5%) as well as the retention rate (80.8% vs 78.5%) were no different between the groups. The fat absorption rate (92.3% vs 91.5%) as well as the weight gain (32.1 vs 31.1 g/day) were similar and there were no differences in the serum parameters studied. The results indicate that feeding VLBW infants with human milk enriched with a well-balanced bovine fortifier fulfil their nutritional requirements as well as diets composed exclusively of human milk protein.

Birth Weight↗

PubMed1993

Phototransformation of monovinyl and divinyl protochlorophyllide by NADPH:protochlorophyllide oxidoreductase of barley expressed in Escherichia coli.

The chlorophyll precursors monovinyl protochlorophyllide (MV-PChlide) and divinyl protochlorophyllide (DV-PChlide) were extracted from mutant C-2A' of the unicellular green alga Scenedesmus obliquus which accumulates both protochlorophyllide derivatives in the dark. The two pigments were characterized by absorption and fluorescence spectroscopy and by plasma desorption mass spectrometry. The molecular masses of MV-PChlide and DV-PChlide were determined as 612 and 610 atomic mass units (amu) respectively. Both MV-PChlide and DV-PChlide were accepted as substrates and photoconverted to chlorophyllides in vitro by NADPH:protochlorophyllide oxidoreductase of barley expressed in Escherichia coli.

Chlorophyta↗

PubMed1993

[Post-conceptional age. Effect on protein requirements of premature infants].

In 12 preterm infants (mean gestational age: 28.9 weeks; mean birthweight: 1230 g) (Group 1) the serum concentrations of urea and alpha-amino-nitrogen were studied during the 32nd and between the 36th and 37th week of post-conceptional age. In 9 preterm infants with a mean gestational age of 34.6 weeks (mean birthweight: 1860 g) (Group 2) the same parameters were estimated during the 36th or 37th week of postconceptional age. In all male infants (group 1: n = 6; group 2: n = 5) the excretion of nitrogen in urine and stools were measured during a 48 h balance period. During the study all infants were fed with human milk enriched with 3 g of a bovine human milk fortifier (Eoprotin, Milupa AG, Germany) per 100 ml human milk (mean protein intake: 3.4 g/kg.day; mean caloric intake: 132.5 kcal/kg.day). Despite the similar protein and energy intakes on all study days the serum concentrations of urea and alpha-amino-nitrogen were significantly higher during the 36th or 37th postconceptional week if compared to those found during the 32nd postconceptional week. This was accompanied by elevated renal excretion of total nitrogen due to an increased excretion of urea in the older infants. The nitrogen excretions in stools were low during both study periods. During the period 36 and 37 weeks of postconceptional age no differences could be found for all parameters studied between the both groups of different gestational ages. The data of the present study suggest that in preterm infants with postconceptional age of 37 weeks or more protein intakes of 3.4 g/kg.day and more may exceed the requirements of these infants. Thus, supplementation of human milk with protein is not necessary after the 37th week of postconceptional age if feeding volumes of 170 ml/kg.day or more are tolerated.

Amino Acids↗

PubMed1992

Postnatal development of liver and exocrine pancreas in polycythemic newborn infants.

In 35 newborn infants appropriate for gestational age the influence of neonatal polycythemia (venous hematocrit greater than 60% measured between the second and fourth hour of life) on development of enterohepatic circulation of bile acids, activities of pancreatic enzymes in duodenal juice, and the effects of hemodilution were studied during the second week of life. A significant correlation was found between the initial hematocrit and both the bile acid concentration in serum and lipase and trypsin activity in duodenal juice. Of 35 infants, 10 were not treated with hemodilution due to asymptomatic polycythemia; they had the highest concentration of serum bile acids associated with the lowest lipase and trypsin activity in duodenal juice. However, the 25 infants treated with hemodilution also showed serum bile acid concentrations and lipase and trypsin activity in duodenal juice out of the normal range when compared to normocythemic infants. These data indicate that, during the first days of life, polycythemia results in a delayed postnatal development of enterohepatic circulation of bile acids and exocrine pancreas functions independently from the occurrence of clinical symptoms. Thus, it can be concluded that, on the first day of life, all polycythemic infants should be treated with hemodilution. Moreover, the nutritional management of these infants must also account for the limited functional capacity of the gastrointestinal tract.

Algorithms↗

PubMed1992

Altered pterin patterns in photobehavioral mutants of Phycomyces blakesleeanus.

Pterins were extracted with methanol from sporangiophores of the lower fungus Phycomyces blakesleeanus and separated and identified by high performance liquid chromatography (HPLC) with fluorescence detection. The following pterins were found and identified for the wild-type strain NRRL1555: carboxypterin (6.7 x 10(-6) M), neopterin (4.2 x 10(-7) M), xanthopterin (5.3 x 10(-6) M), biopterin (3.9 x 10(-7) M), pterin (9.1 x 10(-7) M), and 6,7-dimethylpterin (1.2 x 10(-6) M). The HPLC elution profiles of the wild type were compared to a set of phototropism mutants (genotype mad) with specific defects in the light-transduction pathway. The mutant profiles were qualitatively similar to those of the wild type. Quantitative differences were, however, discerned for madA, madC, and madH mutants. The madA mutation was associated with increased amounts of biopterin and 6,7-dimethylpterin and a reduction of neopterin, pterin, xanthopterin, and unidentified pterins eluting at 14-18 min. The stimulatory effect of the madA mutation on biopterin and 6,7-dimethylpterin appears to be compensated by a secondary mutation (pde) which is responsible for the loss of 75% of adenosine 3',5'-cyclic monophosphate (cAMP)-phosphodiesterase activity. In a madA pde double mutant the amounts of biopterin and 6,7-dimethylpterin fell below the wild-type level. These results suggest that an increased level of endogenous cAMP represses the biosynthesis of these pterins. The madC mutation increased the amounts of biopterin and xanthopterin and that of the unidentified pterins which could be derivatized to carboxypterin. Single madB mutations had, compared to the wild type, two times higher amounts of biopterin and two times lower amounts of neopterin.(ABSTRACT TRUNCATED AT 250 WORDS)

Flavins↗

PubMed1992

Altered flavin patterns in photobehavioral mutants of Phycomyces blakesleeanus.

Flavins were extracted from sporangiophores of the lower fungus Phycomyces blakesleeanus and identified by HPLC with fluorescence detection. In the wild-type strain NRRL1555 they were found to be present at the following concentrations: riboflavin (5.5 x 10(-6) M), flavin mononucleotide (FMN) (4.0 x 10(-6) M) and flavin adenine dinucleotide (1.4 x 10(-6) M). The HPLC elution profiles of the wild type were compared to a set of behavioral mutants (genotype mad) with specific defects in their light-transduction pathway. The photoreceptor mutants C109 (madB), C111 (madB) and L1 (madC) had normal amounts of flavins. The most prominent changes were found in single mutants with a defective madA gene which contained about 25% of riboflavin and about 10% of FMN and FAD normally found in the wild type. A hypertropic mutant with a defective madH gene contained instead 80% of riboflavin and 120% of FMN and FAD. The double mutant L52 (madA madC) and the triple mutant L72 (madA madB madC) had normal amounts of FAD and FMN. This indicates that the madC mutation, which itself causes loss of light sensitivity and which affects the near-UV/blue-light receptor (Galland and Lipson, 1985, Photochem. Photobiol. 41, 331-335) functions as a restorer of the flavin content in a genetic madA background. The double mutant L51 (madA madB) had about 40% of FMN and FAD, suggesting that the madB mutation functions as a partial restorer of flavin content. The photogravitropic thresholds (450 nm) reported for the wild type and the madA and madH mutants were positively correlated to the endogeneous concentrations of FMN and FAD.(ABSTRACT TRUNCATED AT 250 WORDS)

Flavins↗

PubMed1992

[Determination of exocrine pancreatic function in childhood with the pancreozymin-secretin test].

Pancreatic function can only be determined exactly via the pancreozymin-secretin test. We conducted this test in two versions: (1) under conditions of continuous perfusion with the possibility of volume correction and (2) as a simple tubing. We compared the results of 86 tubings with the results of 87 examinations under perfusion. For that purpose all patients were classified into four groups: group a) with 46 and 10 examinations, respectively, in patients suffering from cholestasis in early infancy, group b) with 7 and 12 examinations, respectively, in older patients with liver diseases, group c) with 8 and 17 examinations, respectively, in patients suffering from cystic fibrosis or Shwachman's syndrome and group d) with 25 and 48 examinations, respectively, in children with normal pancreatic function. Both examination methods nearly identical mean values of the enzyme activities in all four patient groups. However, mean variations were found to be higher in case of tubing. Therefore the lower limits (x - 2s) of this test were defined at a lower level than those of the tests under perfusion.

Amylases↗

PubMed1991

Antagonistic blue- and red-light regulation of cab-gene expression during photosynthetic adaptation in Scenedesmus obliquus.

During adaptation of the photosynthetic apparatus of the green alga Scenedesmus obliquus to various light qualities, the accumulation of chlorophylls and pigment-protein complexes (with specific consideration of chlorophyll a/b-binding (Cab) proteins) and cab-gene expression were determined. The fluence rate dependences for chlorophyll accumulation and cab-gene expression were very different. Very low fluence rates of violet (404 nm), blue (461 nm) and red (650 nm) light below the photosynthetic threshold, i.e. between 10(-3) and 10(-1) mumol m-2 s-1, inhibited all of these reactions in cells grown under heterotrophic conditions. At elevated fluence rates (above 1 mumol m-2 s-1), red light retained its negative regulation, whereas blue light stimulated pigment accumulation. Under autotrophic conditions the pattern was more complex, because chlorophyll accumulation was unaffected by light below the photosynthetic threshold. However, the expression of cab-genes was inhibited by red light but stimulated by blue light. Cells adapted to fluence rates, which ensured photosynthetic energy supply (above 1 mumol m-2 s-1), showed an increase in chlorophyll accumulation, blue light being more effective than red light. The results confirm and extend our previous discovery of two antagonistically acting photoreceptors in Scenedesmus which mediate and coordinate the complex functional and structural changes associated with photosynthetic adaptation. One of these receptor pigments is a blue-light receptor with positive action; the other is a violet-red-light receptor which can operate far below the photosynthetic threshold and exerts a negative regulation.

Blotting, Northern↗

PubMed1991

Activities of lipase and trypsin in duodenal juice of infants small for gestational age.

In 18 low birth weight infants, small for gestational age, with different degrees of intrauterine growth retardation the activities of pancreatic lipase and trypsin and the concentrations of bile acids were measured in preprandially aspirated duodenal juice. The results were compared to those of 24 low birth weight infants, appropriate for gestational age, with comparable birth weights and postnatal ages. The activities of both measured pancreatic enzymes were negatively correlated with the degree of intrauterine growth retardation, expressed as the difference between the individual birth weight and the weight of the 10th percentile of the intrauterine growth curve (lipase: r = -0.697, p less than 0.001; trypsin: r = -0.739, p less than 0.001). The activity of trypsin in the small for gestational age infants was within the range of that found in the infants appropriate for gestational age. However, the lipase activity was decreased in infants who presented with growth retardation of greater than 400 g/kg birthweight. The concentrations of bile acids were similar in both groups (4.60 +/- 2.51 and 4.55 +/- 2.26 mmol/L, respectively) and sufficient for activating the bile salt stimulated lipase in human milk. The data suggest that in intrauterine growth retarded infants the lipase activity in the duodenal juice can be a limiting factor for optimal fat digestion. This should be considered in the nutritional management of such infants.

Duodenum↗

PubMed1991

Effects of two antibiotics on hepatic function in low birth weight infants: ampicillin vs. cefotaxime.

In 21 low birth weight infants with two regimens of antibiotic therapy during the first 3 days of life possible hepatotoxic side effects were studied 8 days after the last administration of the tested drugs. Fourteen of the infants were treated with ampicillin/gentamicin and 7 received cefotaxime/gentamicin. The serum concentrations of total bile acids, the activities of transaminases in serum and the cumulative 15N excretion in urine after administration of 3 mg of 15N-labeled methacetin/kg of body weight were used as markers of hepatotoxic side effects. Neither the concentrations of total bile acids (22.6 +/- 12.1 and 19.4 +/- 10.8 mM, respectively) nor the activities of transaminases (alanine aminotransferase, 0.27 +/- 0.06 vs. 0.30 +/- 0.09 mumol/second/liter; aspartate aminotransferase, 0.46 +/- 0.11 vs. 0.49 +/- 0.10 mumol/second/liter) were different between the two groups. In contrast the cumulative 15N excretion in urine was significantly lower in the group treated with cefotaxime/gentamicin than in the group treated with ampicillin/gentamicin (17.2 +/- 6.4 vs. 33.0 +/- 5.1% of intake; P less than 0.01) and also lower than the reported age-related reference values. On the 28th day of life no differences could be found between the cumulative 15N excretion in the urine of the infants treated with cefotaxime/gentamicin and the reported age-related reference values of this test. The results indicate a limited capacity of the monooxygenase system of the liver of low birth weight infants during the first weeks of life and a specific reversible influence of cefotaxime on this hepatocellular system. Further investigations are required to evaluate the clinical relevance of this drug-specific inhibition of the hepatic monooxygenase pathway.

Acetamides↗