Protein-dependent Reduction of the Pyrene Excimer Formation in Membranes

The presence of proteins in lipid bilayers always decreases the excimer formation rate of pyrene and pyrene lipid analogues in a way that is related to the protein-to-lipid ratio. Energy transfer measurements from intrinsic tryptophans to pyrene have shown (Engelke et al., 1994), that in microsomal membranes, the excimer formation rate of pyrene and pyrene fatty acids is heterogeneous within the membrane plane, because a lipid layer of reduced fluidity surrounds the microsomal proteins. This study investigates whether of not liposomes prepared from egg yolk phosphatidylcholine with incorporated gramicidin A give results comparable to those from microsomal membranes. The results indicate that the influence of proteins on the lipid bilayer cannot be described by one unique mechanism: Small proteins such as gramicidin A obviously reduce the excimer formation rate by occupying neighboring positions of the fluorescent probe and thus decrease the pyrene collision frequency homogeneously in the whole membrane plane, while larger proteins are surrounded by a lipid boundary layer of lower fluidity than the bulk lipid. The analysis of the time-resolved tryptophan fluorescence of gramicidin A incorporated liposomes reveals, that the tryptophan quenching by pyrene is stronger for tryptophans located closely below the phospholipid headgroup region because of the pyrene enrichment in this area of the lipid bilayer. Received: 29 December 1996/Revised: 15 May 1996     

Substrates of Energy Metabolism of the Pituitary and Pineal Glands

The capability of the neurohypophysis, the adenohypophysis, and the pineal gland to oxidize nonesterified fatty acids and glucose as energy sources was studied in vivo. Fed and 48-h-starved rats had catheters placed in their femoral vessels. After they became conscious, an intravenous injection of one of the following was given: [1-14C]acetate, [1-14C]octanoate, [1-14C]-palmitate, or [2-14C]glucose. After 5 min the rats were sacrificed. These metabolites produce [14C]acetyl-CoA within the mitochondria when they are oxidized as metabolic fuels. On passage through the Krebs cycle a considerable portion of the 14C is trapped in large amino acid pools closely associated with the Krebs cycle; the appearance of 14C in these amino acids was taken as evidence of oxidation. As expected, brain structures behind the blood-brain barrier (cerebral cortex and caudate) showed considerable labeling of Krebs cycle-associated amino acids in both nutritional states when [2-14C]glucose was the substrate. Surprisingly, however, no label was detected in amino acids of the neurohypophysis or the pineal gland in starved rats and very little in fed rats. On the other hand, 14C from acetate and palmitate was extensively incorporated into amino acids of the pineal gland and the neurohypophysis, while little 14C labeling was found in the cerebral cortex and the caudate. Octanoate, which passes the blood-brain barrier readily, labeled amino acids of all tissues. The experiments demonstrated conclusively that the neural structures studied, which have no blood-brain barrier, do not rely heavily upon glucose as a fuel for oxidative energy metabolism, in contrast to the rest of the brain. The results also showed that nonesterified fatty acids may supply at least some of their energy requirements.     

Changes in the distribution of platelet membrane proteins revealed by energy transfer

The redistribution of platelet membrane proteins in response to platelet activation was studied. To investigate this process we prepared a variety of platelet ligands, including di- and tetrameric concanavalin A, IgG, thrombin, wheat-germ agglutinin and other lectins. These ligands were conjugated either with acceptor (rhodamine isothiocyanate) or donor (fluoresceine isothiocyanate) fluorophore. Platelets exposed to various combinations of ligand species were stimulated with different aggregating agents, and changes in sensitized fluorescence emission or donor quenching were recorded. Energy transfer was observed with thrombin, dimeric concanavalin A after addition of thrombin and various combinations of dimeric concanavalin A with other membrane ligands. The preincubation of platelets with colchicine prevented energy transfer between appropriate ligand pairs and platelet activator. Our studies show that nonradiative energy transfer can be used to analyze redistribution of membrane receptor sites in platelets.     

Regulation of energy flux through the creatine kinase reaction in vitro and in perfused rat heart: 31P-NMR studies

Fluxes catalyzed by soluble creatine kinase (MM) in equilibrium in vitro and by the creatine kinase system in perfused rat hearts were studied by ³¹P-NMR saturation transfer method. It was found that in vitro both forward and reverse fluxes through creatine kinase at equilibrium were almost equal and very stable to changes in $\text{phosphocreatine}\text{creatine}$ ratio (from 0.2 to 3.0) as well as to changes in pH (from 7.4 to 6.5 or 8.1), free Mg²⁺ concentration and 2-fold decrease of total adenine nucleotides and creatine pools (from 8.0 to 4.0 mM and from 30 to 14 mM, respectively). In the rat hearts perfused by the Langendorff method the creatine kinase-catalyzed flux from phosphocreatine to ATP was increased by 50% when oxygen consumption grew from 8 to 55 μmol/min per g of dry wt. due to transition from rest to high workload. These changes could not be exclusively explained on the basis of the equilibrium model by activation of heart creatine kinase due to some decrease in $\text{[}\text{phosphocreatine}\text{]}\text{[}\text{creatine}\text{]}$ ratio (from 1.8 to 0.8) observed during transition from rest to high workload. Analysis of our data showed that an increase in the flux via creatine kinase is correlated with an increase in the rate of ATP synthesis with a linearity coefficient higher than 1.0. These data are more consistent with the concept of energy channeling by phosphocreatine shuttle than with that of the creatine kinase equilibrium in the heart.     

Morphological and functional correlates of VIP neurons in cerebral cortex

Vasoactive Intestinal Polypeptide (VIP) promotes the hydrolysis of ³H-glycogen newly synthesized from ³H-glucose by mouse cortical slices. This effect occurs rapidly, approximately 50% of the maximal effect being reached within one minute. The maximal effect is achieved after 5 minutes and maintained for at least 25 minutes. Furthermore the glycogenolytic effect of VIP is reversible, and pharmacologically specific. Thus several neuropeptides present in cerebral cortex such as cholecystokinin-8, somatostatin-28, somatostatin-14, met-enkephalin, leu-enkephalin, do not affect ³H-glycogen levels. VIP fragments 6–28, 16–28 and 21–28 are similarly inactive. Furthermore, among the peptides which share structural homologies with VIP, such as glucagon, secretin, PHI-27 and Gastric Inhibitory Peptide, only secretin and PHI-27 promote ³H-glycogen hydrolysis, with EC₅₀ of 500 and 300 nM respectively, compared to an EC₅₀ of 25 nM for VIP. Immunohistochemical observations indicate that each VIP-containing bipolar cell is identified with a unique radial cortical volume, which is generally between 15–60 μm in diameter and overlaps with the contiguous domains of neighbouring VIP-containing bipolar cells. Thus this set of biochemical and morphological observations support the notion that VIP neurons have the capacity to regulate the availability of energy substrates in cerebral cortex locally, within circumscribed, contiguous, radial domains.     

Thermodynamics of methylenetetrahydrofolate reduction to methyltetrahydrofolate and its implications for the energy metabolism of homoacetogenic bacteria

The thermodynamics of the methylenetetrahydrofolate reduction to 5-methyltetrahydrofolate was studied with the methylenetetrahydrofolate reductase purified from the homoacetogenic bacterium Peptostreptococcus productus. The equilibrium constants were determined for the forward and backward reactions of methylenetetrahydrofolate reduction with NADH or acetylpyridine adenine dinucleotide (APADH), respectively, as the electron donors. From the equilibrium constants and the known standard redox potentials at pH 7 (E ^o ) of the couples NAD⁺/NADH or APAD⁺/APADH the E ^o of the couple methylene-/methyltetrahydrofolate was determined to be about-200mV. This value is different from values reported before for this couple. The implications for the mechanism of energy conservation of homoacetogens is discussed.Abbreviations FH₄ tetrahydrofolate - CH₂=FH₄ 5,10-methylenetrahydrofolate - CH₃-FH₄ 5-methyltetrahydrofolate - K _eq equilibrium constant - G ^o Gibb's free energy change under standard conditions (all concentrations of reactants = 1 M) - G ^o G ^o at pH 7 ([H⁺]=10^-7 M) - E ^o standard redox potential - G ^o standard redox potential difference of two reactants - E ^o E ^o at pH 7 - R gas constant - F Faraday constant - APAD acetylpyridine adenine dinucleotide (NAD⁺-analogue)     

Control of nitrogenase in chemostat cultures of Rhodobacter capsulatus grown on ammonium at different illuminations

Rhodobacter capsulatus strain 37b4 was grown phototrophically in chemostat cultures with 2 mM of ammonium chloride and 30 mM of malate at a constant dilution rate of 0.075 h^-1. When illumination was raised from 3000 to 30000 lx, steady state biomass levels as well as malate uptake increased linearly with increasing illumination. Yet, in no case external ammonium could be detected in the culture fluid. Specific nitrogenase activity increased by a factor of ten between 3000 and 15000 lx and approached constancy above 15 000 lx. When samples were anaerobically withdrawn from the chemostat and subsequently grown in batch cultures under saturating light conditions, biomass increased to a constant level, independently of the illumination used in the previous chemostat culture. In fact, the specific nitrogen contents of cells were 0.195 and 0.154 (g of N per g of protein) with chemostat cultures adapted to 3000 and 30000 lx, respectively. With the former cultures, specific nitrogen contents decreased to 0.142 g of nitrogen per g of cell protein upon incubation in a batch system. This suggests the existence of free nitrogen compounds in cells of chemostat cultures, the concentrations of which decrease while protein levels increase with increasing energy supply. Intracellular amino acid pools revealed slightly elevated levels of major amino acids in low-light cultures as compared to high-light cultures. On the basis of intracellular levels of ammonium, however, no significant differences could be detected. Since, in addition, malate consumption increased linearly with increasing illumination, it is proposed that light controls nitrogenase in Rhodobacter capsulatus via the C/N ratio, as represented by malate and ammonium consumption, rather than directly.     

Insectivory and its significance to langur diets

Earlier studies on Hanuman langurs (Presbytis entellus) around Jodhpur found them entirely vegetarian (Mohnot, 1974;Winkler, 1988). However, recent observations in the open scrub forests of Jodhpur reveal that scale insects may constitute a regular part of their diet and that insectivory is particularly prevalent in the monsoon months July – September. The insect eating in this habitat seems to support the “Energy/nutrient maximization” hypothesis ofHamilton andBusse (1978).     

“三料”转化与生态农业

农业生态经济系统中,饲料、肥料、燃料作为能流、物流的主要形态和通道,影响着整个系统的结构和功能。本文用源、流、库的关系和数据资料,分析了“三料”转化的重要作用。提出了如何提高其转化效率,促进生态农业建设的技术路线。秸秆资源和腐食食物链的开发是技术关键。     

Management plan for the Royal Society for the Protection of Birds reserve at Dungeness, Kent

THOMAS, G. J., GLOVER, J. & MAKEPEACE, P., 1989. Management plan for the Royal Society for the Protection of Birds reserve at Dungeness, Kent . A synopsis of a new management plan for RSPB Dungeness reserve is presented.