Cloning of the Malic Enzyme Gene from Corynebacterium glutamicum and Role of the Enzyme in Lactate Metabolism

Malic enzyme is one of at least five enzymes, known to be present in Corynebacterium glutamicum, capable of carboxylation and decarboxylation reactions coupling glycolysis and the tricarboxylic acid cycle. To date, no information is available concerning the physiological role of the malic enzyme in this bacterium. The malE gene from C. glutamicum has been cloned and sequenced. The protein encoded by this gene has been purified to homogeneity, and the biochemical properties have been established. Biochemical characteristics indicate a decarboxylation role linked to NADPH generation. Strains of C. glutamicum in which the malE gene had been disrupted or overexpressed showed no detectable phenotype during growth on either acetate or glucose, but showed a significant modification of growth behavior during lactate metabolism. The wild type showed a characteristic brief period of exponential growth on lactate followed by a linear growth period. This growth pattern was further accentuated in a malE-disrupted strain (ΔmalE). However, the strain overexpressing malE maintained exponential growth until all lactate had been consumed. This strain accumulated significantly larger amounts of pyruvate in the medium than the other strains.     

Preliminary X-ray data for an N-terminal fragment of rabbit serum transferrin

An iron-containing fragment (Mr approximately 39,000) of rabbit serum transferrin has been crystallized from a solution of 25% (w/v) polyethylene glycol 6000, 50 mM-disodium piperazine-N,N'bis(2-ethanesulphonate) adjusted to pH 6.0 at 4 degrees C. The space group is P3(1)21 (or the enantiomorph) with a = b = 66.8(1) A, c = 137.5(3) A and Z = 6. The crystals appear as hexagonal plates, with the unique axis perpendicular to the plate. The crystals, kept at 4 degrees C, are stable in the X-ray beam for at least 130 hours and diffract to better than 1.8 A resolution.     

Green Sturgeon Distribution in the Pacific Ocean Estimated from Modeled Oceanographic Features and Migration Behavior

The green sturgeon (Acipenser medirostris), which is found in the eastern Pacific Ocean from Baja California to the Bering Sea, tends to be highly migratory, moving long distances among estuaries, spawning rivers, and distant coastal regions. Factors that determine the oceanic distribution of green sturgeon are unclear, but broad-scale physical conditions interacting with migration behavior may play an important role. We estimated the distribution of green sturgeon by modeling species-environment relationships using oceanographic and migration behavior covariates with maximum entropy modeling (MaxEnt) of species geographic distributions. The primary concentration of green sturgeon was estimated from approximately 41–51.5° N latitude in the coastal waters of Washington, Oregon, and Vancouver Island and in the vicinity of San Francisco and Monterey Bays from 36–37° N latitude. Unsuitably cold water temperatures in the far north and energetic efficiencies associated with prevailing water currents may provide the best explanation for the range-wide marine distribution of green sturgeon. Independent trawl records, fisheries observer records, and tagging studies corroborated our findings. However, our model also delineated patchily distributed habitat south of Monterey Bay, though there are few records of green sturgeon from this region. Green sturgeon are likely influenced by countervailing pressures governing their dispersal. They are behaviorally directed to revisit natal freshwater spawning rivers and persistent overwintering grounds in coastal marine habitats, yet they are likely physiologically bounded by abiotic and biotic environmental features. Impacts of human activities on green sturgeon or their habitat in coastal waters, such as bottom-disturbing trawl fisheries, may be minimized through marine spatial planning that makes use of high-quality species distribution information.     

Physiology of pyruvate metabolism in Lactococcus lactis

Lactococcus lactis, a homofermentative lactic acid bacterium, has been studied extensively over several decades to obtain sometimes conflicting concepts relating to the growth behaviour. In this review some of the data will be examined with respect to pyruvate metabolism. It will be demonstrated that the metabolic transformation of pyruvate can be predicted if the growth-limiting constraints are adequately established. In general lactate remains the major product under conditions in which sugar metabolism via a homolactic fermentation can satisfy the energy requirements necessary to assimilate anabolic substrates from the medium. In contrast, alternative pathways are involved when this energy supply becomes limiting or when the normal pathways can no longer maintain balanced carbon flux. Pyruvate occupies an important position within the metabolic network of L. lactis and the control of pyruvate distribution within the various pathways is subject to co-ordinated regulation by both gene expression mechanisms and allosteric modulation of enzyme activity.     

Maintaining a controlled residual growth capacity increases the production of polyhydroxyalkanoate copolymers by Alcaligenes eutrophus

Summary The manner in which copolymer poly(HB-co-HV) production was influenced by different methods of limiting cell proliferation during the production phase was examined. Polymer production was significantly improved in fermentation strategies in which some growth was maintained, either by linear or exponential nitrogen source feeding as compared to cultures in which nitrogen supply was totally interrupted. Improved volumetric productivities were obtained in cultures fed with NH₄OH and the proportion of 3HV incorporated was approximately twofold higher in these cultures. These performance improvements were due to higher specific rates of glucose and propionate consumption in cultures in which true growth capacity was maintained.     

Growth and energetics of Leuconostoc mesenteroides NRRL B-1299 during metabolism of various sugars and their consequences for dextransucrase production.

The metabolic and energetic properties of Leuconostoc mesenteroides have been examined with the goal of better understanding the parameters which affect dextransucrase activity and hence allowing the development of strategies for improved dextransucrase production. Glucose and fructose support equivalent specific growth rates (0.6 h-1) under aerobic conditions, but glucose leads to a better biomass yield in anaerobiosis. Both sugars are phosphorylated by specific hexokinases and catabolized through the heterofermentative phosphoketolase pathway. During sucrose-grown cultures, a large fraction of sucrose is converted outside the cell by dextransucrase into dextran and fructose and does not support growth. The other fraction enters the cell, where it is phosphorylated by an inducible sucrose phosphorylase and converted to glucose-6-phosphate (G-6-P) by a constitutive phosphoglucomutase and to heterofermentative products (lactate, acetate, and ethanol). Sucrose supports a higher growth rate (0.98 h-1) than the monosaccharides. When fructose is not consumed simultaneously with G-1-P, the biomass yield relative to ATP is high (16.8 mol of ATP.mol of sucrose-1), and dextransucrase production is directly proportional to growth. However, when the fructose moiety is used, a sink of energy is observed, and dextransucrase production is no longer correlated with growth. As a consequence, fructose catabolism must be avoided to improve the amount of dextransucrase synthesized.     

Simultaneous consumption of glucose and fructose from sugar mixtures during batch growth of Corynebacterium glutamicum

Growth of Corynebacterium glutamicum on mixtures of glucose and fructose leads to simultaneous consumption of both sugars in which the uptake of each sugar is directly related to the expression of the corresponding sugar uptake mechanism. The overall rate of sugar uptake was higher on sugar mixtures than on either glucose or fructose alone and was similar to that observed during sucrose metabolism. The results suggest that sugar uptake limits metabolic rates though, in the case of fructose, overflow metabolism of both lactate and dihydroxyacetone was observed. Such products could reflect a higher flux through glycolysis rather than the pentose pathway during catabolism of fructose. Received: 24 October 1996 / Received revision: 10 January 1997 / Accepted: 10 January 1997     

An X-ray structural study of human ceruloplasmin in relation to ferroxidase activity

The role of ceruloplasmin as a ferroxidase in the blood, mediating the release of iron from cells and its subsequent incorporation into serum transferrin, has long been the subject of speculation and debate. However, a recent X-ray crystal structure determination of human ceruloplasmin at a resolution of around 3.0?Å, in conjunction with studies associating mutations in the ceruloplasmin gene with systemic haemosiderosis in humans, has added considerable weight to the argument in favour of a ferroxidase role for this enzyme. Further X-ray studies have now been undertaken involving the binding of the cations Co(II), Fe(II), Fe(III), and Cu(II) to ceruloplasmin. These results give insights into a mechanism for ferroxidase activity in ceruloplasmin. The residues and sites involved in ferroxidation are similar to those proposed for the heavy chains of human ferritin. The nature of the ferroxidase activity of human ceruloplasmin is described in terms of its three-dimensional molecular structure.     

The reactivity of the disulphide bonds of wool

1. Fully reduced and S-carboxymethylated wool samples were prepared in which either the readily reducible cystine bonds or those that could only be reduced with difficulty were specifically labelled with iodo[2-(14)C]acetate; these two cystine fractions correspond to the (A+B) and (C+D) cystine fractions respectively, of Middlebrook & Phillips (1942). 2. Radioactively labelled peptides were isolated from partial acid hydrolysates of these wool samples. 3. It appears that the (A+B) cystine residues probably owe their increased reactivity to being in a more polar environment. 4. The implication of these results for the problem of characterizing the disulphide bonds of wool is briefly discussed.