Ornithine decarboxylase properties: Is there a role for a microsome-bound inactivating activity?

Liver microsomes have a strong ornithine decarboxylase (ODC) inactivating capacity in vitro. The present results suggest that this may be involved in regulation of ODC activity in vivo: (1) the ODC inactivating capacity of microsomes appears susceptible to in vivo modulation: a single administration of thioacetamide, which induces ODC, also causes a significant increase in the inactivating capacity of the microsomes; (2) under conditions leading to increased microsome-bound ODC-inactivating capacity (e.g. liver from thioacetamide-treated rates versus regenerating liver) ODC displays a greater thermal lability and inactivability in vitro. A possible involvement of this microsomal activity in an autoregulatory pathway of ODC is suggested by the fact that it is induced by the administration of polyamines. However, inhibition of ODC activity by alpha-difluoromethylornithine does not prevent the increase of the microsomal activity caused by thioacetamide. Thus, polyamine biosynthesis does not appear to be an absolute requirement for induction of the microsomal ODC-inactivating capacity. The apparent half-life of ODC in vivo, as evaluated after cycloheximide administration, does not appear to correlate with the microsomal ODC-inactivating capacity content and the stability properties of ODC in vitro.     

The relationship of 4-aminobutyric acid metabolism to ammoniagenesis in renal cortex

Mitochondrial 4-aminobutyrate aminotransferase in rat kidney can utilize pyruvate as the acceptor for the amino group of 4-aminobutyrate. Renal 4-aminobutyrate aminotransferase activity at saturating equimolar concentration of 4-aminobutyrate and 5 mM pyruvate is 42.8 ± 2.5 μmol/g protein per h (mean ± S.E.M.) or 70% of 4-aminobutyrate aminotransferase activity with equimolar α-ketoglutarate. 4-Aminobutyrate aminotransferase in brain does not transaminate with pyruvate. Since pyruvate is an important mitochondrial metabolite in kidney, net disposal of glutamate via the 4-aminobutyrate pathway is possible. The renal 4-aminobutyrate pathway in the rat has other distinctive features when compared with the pathway in rat brain. Most inhibitors of rat neuronal glutamate decarboxylase were ineffective against the renal form of the enzyme, but 20 mM semicarbazide inhibited the latter form by 80% (P < 0.001) in vitro and reduced renal 4-aminobutyrate content by 75% (P < 0.001) in vivo. In the presence of 20 mM semicarbazide, ammoniagenesis by rat renal cortex slices incubated in 1 mM glutamine was inhibited 26% (P < 0.01). Semicarbazide was proportionately less effective (15% inhibition) when ammoniagenesis was stimulated (+243%) in slices prepared from chronically acidotic animals, and was no deterrant to ammoniagenesis when non-acidotic slices were incubated in supraphysiologic concentrations of 10 mM glutamine. We conclude that whereas integrity of the renal 4-aminobutyrate pathway may contribute to glutamate disposal and thus ammoniagenesis under physiologic conditions, the pathway is a passive participant in the overall process of ammoniagenesis.     

User−Producer Interaction in Housing Energy Innovations

Von Hippel and colleagues have highlighted the crucial role of users in innovation in different industries and types of products. They describe the innovation process in terms of the distinct domains of knowledge that producers and users possess. Producers have knowledge about technical solutions and users about their needs, the context of use, and their own capabilities as users. Both sets of knowledge are characterized by "stickiness": They move relatively freely within their own domain but are difficult to transfer outside of it.
In the case of radical innovations for sustainable consumption, the problem of "sticky information" is compounded. Both producers and consumers need to reach out of their conventional competencies and search for new solutions. "Societal actors," such as government bodies or environmental experts, can show the way to such solutions, but this new knowledge needs to be integrated with the "sticky" knowledge about everyday practices in production and consumption.
In the present article we attempt to conceptualize the role and interaction of user and producer knowledge with the knowledge of environmental experts in housing energy innovations. We do so by applying the user−producer interaction framework to a case study on the introduction of low-energy housing concepts in Finland. On the basis of this analysis, we draw conclusions on the potential and limitations of today's practices in the field. For example, we suggest that user involvement can help to enhance the acceptance of low-energy solutions but that the methods for involving users need to be adapted to the particular circumstances in each industry.     

Nucleotide sequence of the gene encoding the Corynebacterium glutamicum mannose enzyme II and analyses of the deduced protein sequence

Abstract The complete nucleotide sequence of the gene encoding the Corynebacterium glutamicum mannose enzyme II (EII^Man) was determined. The gene consisted of 2052 base pairs encoding a protein of 683 amino acid residues; the molecular mass of the protein subunit was calculated to be 72570 Da. The N-terminal hydrophilic domain of EII^Man showed 39.7% homology with a C-terminal hydrophilic domain of Escherichia coli glucose-specific enzyme II (EII^Glc). Similar homology was shown between the C-terminal sequence of EII^Man and the E. coli glucose-specific enzyme III (EIII^Glc), or the EIII-like domain of Streptococcus mutans sucrose-specific enzyme II. Sequence comparison with other EIIs showed that EII^Man contained residues His-602 and Cys-28 which were homologous to the potential phosphorylation sites of EIII^Glc, or EIII-like domains, and hydrophilic domains (IIB) of several EIIs, respectively.     

Enhanced glucose consumption in erythrocytes under mechanical stress

In this paper we study the question of whether the unique features of erythrocyte (biconcave shape, extremely high deformability etc.) result only from the specific structural characteristics of the membrane or whether the maintenance of these features is conditioned by the supply of chemical energy. It is shown that glucose, the main source of cell energy, is consumed at a markedly increased rate when there is appreciable mechanical stress of the cell. This observation supports the hypothesis that there is utilization of chemical energy for the mechanical needs of the membrane.     

The gelling of κ-carrageenan in light and heavy water

Gels of κ-carrageenan were prepared in H₂O and D₂O. Rheological measurements revealed that in heavy water the elastic modulus is substantially higher. From the rheological view point, this result indicates the formation of a higher number of physical-crosslinking points in the structure of the gel. These crosslinking points are mainly associated with the aggregation of the double-helix of the κ-carrageenan, which is enhanced in D₂O. The thermal stability of the gels in both solvents (relative to the sol-gel transition) was also investigated by using polarimetric measurements (to measure the relative fraction of helix-coil) and micro-differential scanning calorimetry (micro-DSC). The results obtained using these techniques are very consistent and allow us to propose a model to explain the differences for the gels formed in light and heavy water based on the degree of double-helix aggregation.     

Strategy combining chiral chromatography with β-cyclodextrin and stereospecific enzyme reaction detection with hydroxysteroid dehydrogenases for resolving steroid epimers

Steroids are chiral molecules with multiple stereogenic centers. Studies of their intermediary metabolism often require analytical techniques to separate the isomers and determine their stereochemistry. Methods for resolving steroid stereoisomers by HPLC using β-cyclodextrin in the mobile phase are reported. Even with the improved selectivity of cyclodextrin chromatography, not all isomers within a steroid series can be resolved. Additional specificity is achieved by reaction detection using postcolumn reactors containing hydroxysteroid dehydrogenases stereospecific for the configuration of the hydroxy functions of steroids. The enzymes catalyze the oxidation of hydroxysteroids and reduction of the coenzyme NAD to NADH. NADH, which is highly fluorescent, is detected at the nanogram levels. Isomers not separated by chromatography were effectively resolved by reaction detection with stereospecific enzymes. © 1992 Wiley-Liss, Inc.     

Green microalgae can use naphthalenesulfonic acids as sources of sulfur

1-Naphthalenesulfonate (1-NS) was utilized by axenic cultures of Scenedesmus obliquus and by 5 other green microalgae as the sole source of sulfur. For all algae under study, 2-naphthalenesulfonate was definitely inferior to 1-NS as a source of sulfur. The rate of disapperance of 1-NS from the medium was measured by HPLC and, indirectly, by relating growth to sulfur supply. The physiological availability of 1-NS sulfur for Scenedesmus obliquus amounted to about 14% of sulfate sulfur. 1-Naphthol appeared as the major metabolite of 1-NS. Hence, it was concluded that 1-NS underwent a desulfonation which also took place in the presence of moderate concentrations of sulfate.Abbreviations HPLC high performance liquid chromatography - 1-NS 1-naphthalenesulfonic acid - 2-NS 2-naphthalenesulfonic acid - OD optical density - OD₀ optical density at time 0 of the light-and-dark cycle Dedicated to Prof. Dr. W. Habsguth on the occasion of his 75th birthday     

Extracellular matrix metabolism by chondrocytes 7. Evidence that L-glutamine is an essential amino acid for chondrocytes and other connective tissue cells

THe incorporation of [³H]glycine into acid-insoluble protein and of [³H]acetate into glysoaminoglycans by cultured chick chondrocytes was stimulated by the addition of L-glutamine to the incubation medium. The effect of exogenous L-glutamine on protein synthesis was studied further by examining changes in the sedimentation patterns on sucrose gardients of ribosomes isolated from chondrocytes incubated in presence and absence of L-glutamine. It was found that the absence of L-glutamine caused a disaggregation of poly-ribosomes that was reversed by the addition of this amino acid to the culture medium. No detectable glutamine synthetase activity could be measured in avian articular cartilage. These results indicate that L-glutamine is an essential amino acid for cartilage in that an extracellular supply of this amino acid is required for the maintenance of protein and glycosaminoglycan synthesis. A dependence on L-glutamine was also demonstrated for other avain connective tissues.     

Alteration of Neuroblastoma Ganglioside Metabolism by Retinoic Acid

Cellular differentiation is often associated with striking changes in ganglioside metabolism. Because retinoic acid causes cellular differentiation in vitro, we have characterized its effect on ganglioside synthesis and shedding by LAN-5 human neuroblastoma cells. Three major observations were made: (a) 20 microM retinoic acid caused a marked (twofold) increase in cellular ganglioside content, with a slight relative enhancement in GD1a and GT1b synthesis, (b) ganglioside shedding increased in parallel with increased cellular ganglioside content, and also, unexpectedly, (c) retinoic acid caused a quantitatively similar increase in content of cell membrane phospholipids, which are also shed. We conclude that enhanced ganglioside synthesis and shedding by retinoic acid are part of a previously undescribed generalized stimulatory effect on membrane lipid metabolism.