The molecular mechanism for the tetrameric association of glycogen phosphorylase promoted by protein phosphorylation.

The allosteric transition of glycogen phosphorylase promoted by protein phosphorylation is accompanied by the association of a pair of functional dimers to form a tetramer. The conformational changes within the dimer that lead to the creation of a protein recognition surface have been analyzed from a comparison of the crystal structures of T-state dimeric phosphorylase b and R-state tetrameric phosphorylase a. Regions of the structure that participate in the tetramer interface are situated within structural subdomains. These include the glycogen storage subdomain, the C-terminal subdomain and the tower helix. The subdomains undergo concerted conformational transitions on conversion from the T to the R state (overall r.m.s. shifts between 1 and 1.7 A) and, together with the quaternary conformational change within the functional dimer, create the tetramer interface. The glycogen storage subdomain and the C-terminal subdomain are distinct from those regions that contribute to the dimer interface, but shifts in the subdomains are correlated with the allosteric transitions that are mediated by the dimer interface. The structural properties of the tetramer interface are atypical of an oligomeric protein interface and are more similar to protein recognition surfaces observed in protease inhibitors and antibody-protein antigen complexes. There is a preponderance of polar and charged residues at the tetramer interface and a high number of H-bonds per surface area (one H-bond per 130 A2). In addition, the surface area made inaccessible at the interface is relatively small (1,142 A2 per subunit on dimer to tetramer association compared with 2,217 A2 per subunit on monomer-to-dimer association).     

The development of granulation in an upflow floc digester and an upflow anaerobic sludge blanket digester treating cane juice stillage

Summary The use of synthetic polyelectrolytes in the Upflow Floc digester during the treatment of high strength cane juice stillage, resulted in a more rapid accumulation of biomass and promoted granule formation at an earlier stage compared to a control upflow anaerobic sludge blanket digester (UASB). In the Upflow Floc reactor the granules were composed of rod shaped organisms, whereas in the UASB the granules were primarily filamentous. Both types of granules had good settling properties and high activities.     

Structured modelling of animal cells

Recent advances in computer technology have promoted the design and use of detailed, computer-based models for biological systems. For many non-biological systems, the complexity of such simulations may be considered inappropriate and unwieldy, but in biological systems, and more specifically in animal cell culture, this level of complexity simply mimics what is only beginning to be understood about metabolic processs. With this in mind, we contend that complex, structured models are vital tools in the investigation of fundamental biological processes. An example of such a simulation, which describes the commercial production of therapeutic proteins by animal cell cultures, is considered.     

Carbohydrate and amino acid metabolism during batch culture of a human lymphoblastoid cell line,BTSN6

This work presents data on the carbohydrate and amino acid metabolism of a lymphoblastoid cell line producing an IgG1 antibody. In static culture, it was observed that lactate levels were significantly lowered when the cells were cultured on galactose as a carbon source. The use of carbohydrate substitution may be useful in lowering lactate levels, if it is established that this component is toxic to the cells. In addition, carbohydrate substitution may be used to modify glycosylation patterns and hence pharmacokinetic properties of glycoproteins.The amino acids glutamine and tryptophan were shown to be limiting in batch culture on this medium (DR, a 1:1 mixture of DMEM and RPMI, with 4mM glutamine). Amino acids produced included alanine, proline and glutamate. Serine was consumed to exhaustion, which was followed by a depletion of extracellular glycine. Amino acid metabolism, specific antibody productivity and specific growth rate were shown to be functions of the inoculation density in stirred flask culture. The results have implications for the design of media for both low and high density antibody manufacture by these cell lines.     

Simulation and dynamic optimisation of animal cell culture

In animal cell culture, there are some 25 substrates that both have a significant effect on the culture performance and which can be measured with relative ease. A detailed dynamic simulation for such a culture has been produced and an optimisation policy that use this model to identify ideal media conditions has been developed. This paper describes an extension of that work to include the dynamic optimisation of cultures under fed-batch operation. Two different types of feeding policy were considered – in the first, discrete shots of feed were supplied, while in the second, feed was added continuously. Both policies offered significant improvements in the predicted productivity of the culture - up to 30% that of an experimentally optimisedbatch culture.     

Inhibition of dihydropteridine reductase by dopamine

Dihydropteridine reductase has been purified 900-fold from rat liver. Dopamine inhibited the enzyme up to 50% at a concentration of 0.11mm. In the presence of dopamine the enzyme gave non-hyperbolic v-against-[S] plots. This enzyme may have a role in control of dopamine biosynthesis.     

Biliary excretion of some anionic derivatives of diethylstilboestrol and phenolphthalein in the guinea pig.

The metabolic fates and modes of excretion of diethylstilboestrol mono[35S]sulphate and diethylstilboestrol di[35S]sulphate were studied in the guinea pig. Comparative studies were also made with [G-3H]diethylstilboestrol and phenolphthalein di[35S]sulphate. Diethylstiboesterol di[35S]sulphate was extensively eliminated in the bile unchanged. After administration of diethylstilboestrol mono[35S]sulphate, extensive biliary elimination of radioactivity was also recorded. Radioactive components were identified as diethylstilboestrol disulphate, diethylstilboestrol monosulphate monoglucuronide and unchanged diethylstilboestrol monosulphate. When [G-3H]diethylstilboestrol was administered, 3H-labelled diethylstilboestrol monoglucuronide, diethylstilboestrol monosulphate monoglucuronide and diethylstilboestrol disulphate appeared in the bile. Phenolphthalein di[35S]sulphate was excreted unchanged in bile. These findings are discussed in relation to studies carried out in the rat [Barford, Olavesen, Curtis & Powell (1977) Biochem. J. 164, 423--430] and species differences are related to differences in enzyme activities in rat and guinea-pig liver.     

Design of laboratory continuous-culture equipment for accurate gaseous metabolism measurements

The accuracy of kinetic and stoichiometric data obtained from most laboratory-scale continuous-culture equipment, particularly involving gaseous measurements, may be much lower than many workers realize, despite the use of good quality instruments. For example, errors in specific oxygen uptake measurements (QO(2)) easily can be as high as +/-100%. This article assesses the accuracies of individual instruments and of the overall system in greater detail than has previously been reported and suggestions are made as to how the errors can be reduced to acceptable levels.     

A new model of uptake of multiple sugars by S. cerevisiae

Carrying on from our work with yeast in batch culture with mixed substrates of glucose and fructose, a model developed previously was modified to incorporate firstly the use of sucrose as substrate and secondly the ability to simulate continuous culture. Experiments using sucrose as the limiting substrate were simulated based on sugar uptake, biomass and ethanol production, carbon dioxide production and oxygen consumption. The new sugar uptake models were able to successfully simulate these experiments. On the basis of these experiments there is a strong suggestion that a proportion of the sucrose utilised is transported into the cell rather than hydrolysed prior to entry. Continuous culture experiments were also simulated by adapting the modelling program into the format of a multiple differential equation problem solver called SPEEDUP.     

Further characterization of the binding of human recombinant interleukin 2 to heparin and identification of putative binding sites

We have previously provided compelling evidence that human recombinant interleukin 2 (IL-2) binds to the sulfated polysaccharides heparin, highly sulfated heparan sulfate and fucoidan. Here we show that IL-2 binding is dependent on heparin chain length, but with fragments as small as 15-mers retaining binding activity. The addition of exogenous heparin has no effect on the in vitro biological activity of IL-2. In addition soluble IL-2 receptor alpha and beta polypeptides do not compete with heparin for the binding of IL-2. IL-2 bound by heparin is still recognized by two IL-2 specific monoclonal antibodies, 3H9 and H2- 8, whose epitopes lie in the amino terminal region. Murine IL-2 unlike its human counterpart fails to bind to heparin. Human IL-2 analogs with single amino acid substitutions at positions Lys43, Thr51, and Gln126 analogs no longer bind to heparin. By contrast the Arg38Ala analog retains heparin full heparin binding activity. These experimental findings together with molecular modeling studies suggest two putative heparin binding sites on human IL-2, one involving four basic residues, Lys48, Lys49, Lys54, and His55, and the other being a discontinuous site comprising Lys43, Lys64, Arg81, and Arg83. Neither of these two clusters is completely conserved in murine IL-2. Overall our data suggest that the binding of human IL-2 to heparin and heparan sulfate does not interfere with IL-2/IL-2 receptor interactions. Therefore, binding to glycosaminoglycan may be a mechanism for retaining the cytokine in an active form close to its site of secretion in the tissue, thus favoring a paracrine role for IL-2.