Georg Wilhelm Löhr

Bio: Georg Wilhelm Löhr is an academic researcher. The author has contributed to research in topics: Enzyme & Dehydrogenase. The author has an hindex of 2, co-authored 2 publications receiving 1285 citations.

Glucose-6-phosphate Dehydrogenase

Abstract: Publisher Summary This chapter discusses glucose-6-phosphate dehydrogenase (G6P-DH), which was first isolated from erythrocytes and from fermenting yeast by Warburg et al., who carried out an extensive purification and characterization of the enzyme. Blood cells, adipose tissue, and lactating mammary gland are especially rich sources of the enzyme. Some human and animal tumors contain high activity of the enzyme. G6P-DH is applied in biochemistry and clinical chemistry. Triethanolamine buffer (50 mM, pH 7.5) containing 5 mM EDTA has proved best. Measurements are made on tissue samples with 0.67 mM G-6-P and 0.5 mM NADP, which are optimum concentrations for the enzyme from erythrocytes. G6P-DH is inhibited by primaquine and other 8-aminoquinolines (antimalarial drugs) in millimolar concentration, as well as by phenylhydrazine. Nevertheless, the therapeutic concentration of these substances is more than tenfold lower and therefore, they have no significant effect on the measurements.

Glucose-6-phosphate Dehydrogenase: (Zwischenferment)

Abstract: Publisher Summary This chapter describes the preparation and stability of glucose-6-phosphate dehydrogenase (G6P-DH). G6P-DH was first isolated from erythrocytes and by fermenting yeast. It has been demonstrated in practically all animal tissues and in micro-organisms. Blood cells, adipose tissue, and the lactating mammary gland that are especially rich sources of the enzyme. Some human and animal tumors contain a high concentration of this enzyme. The optimum pH of the G6P-DH reaction is 8.3 for the enzyme from yeast or blood cells. It is found that between pH 7.4 and 8.6 there is little change in the enzyme activity. The measurements are made at pH 7.5 because this is nearest to physiological conditions and allows comparison to be made with other enzyme activities which are usually measured at this pH. The accuracy of the determination of activity in liver tissue can be increased if the hemoglobin content of the supernatant is estimated, and on the basis of this estimation, the additional G6P-DH is calculated. This value is subtracted from the total G6P-DH activity of the liver homogenate.

Tolerance of pea (Pisum sativum L.) to long‐term salt stress is associated with induction of antioxidant defences

Abstract: Using two cultivars of Pisum sativum L. with different sensitivity to NaCl, the effect of long-term (15 d) NaCl (70 m M) treatments on the activity and expression of the foliar ascorbate–glutathione cycle enzymes, superoxide dismutase isozymes and their mRNAs was evaluated and related to their ascorbate and glutathione contents. High-speed supernatant (soluble) fractions, enriched for cytosolic components of the antioxidant system, were used. In this fraction from the NaCl-tolerant variety (cv Granada), the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), Mn-superoxide dismutase (Mn-SOD) and dehydroascorbate reductase (DHAR) increased, while CuZn-SOD activity remained constant. In the NaCl-sensitive plants (cv Challis), salinity did not produce significant changes in APX, MDHAR and GR activities. Only DHAR activity was induced in cv Challis, whereas soluble CuZn-SOD activity decreased by about 35%. Total ascorbate and glutathione contents decreased in both cultivars, but the decline was greater in NaCl-sensitive plants. This difference between the two cultivars was more pronounced when the transcript levels of some these enzymes were examined. Transcript levels for mitochondrial Mn-SOD, chloroplastic CuZn-SOD and phospholipid hydroperoxide glutathione peroxidase (PHGPX), cytosolic GR and APX were strongly induced in the NaCl-tolerant variety but not in the NaCl-sensitive variety. These data strongly suggest that induction of antioxidant defences is at least one component of the tolerance mechanism of peas to long-term salt-stress.

The return of metabolism: biochemistry and physiology of the pentose phosphate pathway

Abstract: The pentose phosphate pathway (PPP) is a fundamental component of cellular metabolism. The PPP is important to maintain carbon homoeostasis, to provide precursors for nucleotide and amino acid biosynthesis, to provide reducing molecules for anabolism, and to defeat oxidative stress. The PPP shares reactions with the Entner-Doudoroff pathway and Calvin cycle and divides into an oxidative and non-oxidative branch. The oxidative branch is highly active in most eukaryotes and converts glucose 6-phosphate into carbon dioxide, ribulose 5-phosphate and NADPH. The latter function is critical to maintain redox balance under stress situations, when cells proliferate rapidly, in ageing, and for the 'Warburg effect' of cancer cells. The non-oxidative branch instead is virtually ubiquitous, and metabolizes the glycolytic intermediates fructose 6-phosphate and glyceraldehyde 3-phosphate as well as sedoheptulose sugars, yielding ribose 5-phosphate for the synthesis of nucleic acids and sugar phosphate precursors for the synthesis of amino acids. Whereas the oxidative PPP is considered unidirectional, the non-oxidative branch can supply glycolysis with intermediates derived from ribose 5-phosphate and vice versa, depending on the biochemical demand. These functions require dynamic regulation of the PPP pathway that is achieved through hierarchical interactions between transcriptome, proteome and metabolome. Consequently, the biochemistry and regulation of this pathway, while still unresolved in many cases, are archetypal for the dynamics of the metabolic network of the cell. In this comprehensive article we review seminal work that led to the discovery and description of the pathway that date back now for 80 years, and address recent results about genetic and metabolic mechanisms that regulate its activity. These biochemical principles are discussed in the context of PPP deficiencies causing metabolic disease and the role of this pathway in biotechnology, bacterial and parasite infections, neurons, stem cell potency and cancer metabolism.

Energy metabolism in human pluripotent stem cells and their differentiated counterparts.

Abstract: Background Human pluripotent stem cells have the ability to generate all cell types present in the adult organism, therefore harboring great potential for the in vitro study of differentiation and for the development of cell-based therapies. Nonetheless their use may prove challenging as incomplete differentiation of these cells might lead to tumoregenicity. Interestingly, many cancer types have been reported to display metabolic modifications with features that might be similar to stem cells. Understanding the metabolic properties of human pluripotent stem cells when compared to their differentiated counterparts can thus be of crucial importance. Furthermore recent data has stressed distinct features of different human pluripotent cells lines, namely when comparing embryo-derived human embryonic stem cells (hESCs) and induced pluripotent stem cells (IPSCs) reprogrammed from somatic cells.

The power to reduce: pyridine nucleotides – small molecules with a multitude of functions

Abstract: The pyridine nucleotides NAD and NADP play vital roles in metabolic conversions as signal transducers and in cellular defence systems. Both coenzymes participate as electron carriers in energy transduction and biosynthetic processes. Their oxidized forms, NAD + and NADP + , have been identified as important elements of regulatory pathways. In particular, NAD + serves as a substrate for ADP-ribosylation reactions and for the Sir2 family of NAD + -dependent protein deacetylases as well as a precursor of the calcium mobilizing molecule cADPr (cyclic ADP-ribose). The conversions of NADP + into the 2′-phosphorylated form of cADPr or to its nicotinic acid derivative, NAADP, also result in the formation of potent intracellular calcium-signalling agents. Perhaps, the most critical function of NADP is in the maintenance of a pool of reducing equivalents which is essential to counteract oxidative damage and for other detoxifying reactions. It is well known that the NADPH/NADP + ratio is usually kept high, in favour of the reduced form. Research within the past few years has revealed important insights into how the NADPH pool is generated and maintained in different subcellular compartments. Moreover, tremendous progress in the molecular characterization of NAD kinases has established these enzymes as vital factors for cell survival. In the present review, we summarize recent advances in the understanding of the biosynthesis and signalling functions of NAD(P) and highlight the new insights into the molecular mechanisms of NADPH generation and their roles in cell physiology.