Choline kinase and ethanolamine kinase are separate, soluble enzymes in rat liver.

Choline kinase and ethanolamine kinase are located in the cytosol from rat liver and have been copurified more than 500-fold by affinity chromatography [P. J. Brophy and D. E. Vance (1976) FEBS Lett. 62, 123-125]. Kinetic properties of the two activities were determined. Choline kinase had a Km for choline of 0.033 mM and ethanolamine was a competitive inhibitor (Ki = 6.2 mM). Ethanolamine kinase had a Km for ethanolamine of 7.7 mM and choline was a 'mixed' type of inhibitor with a Ki of 0.037 mM. Both enzymes activities responded in a similar fashion to the adenylate energy charge. Betaine and choline phosphate partially inhibited both kinases with a 93% inhibition of the ethanolamine kinase by 5 mM choline phosphate. CTP and ethanolaminephosphate partially inhibited the ethanolamine kinase, but not the choline kinase. Other metabolites tested had negliglible effects on both kinases. The affinity-column-purified enzyme was analyzed by disc gel electrophoresis which resolved the two activities. Hence, although many of the properties of the two activities are similar, choline kinase and ethanolamine kinase must be separate enzymes. Analysis of rat liver cytosol by disc gel electrophoresis indicated four isoenzymes for choline kinase and ethanolamine kinase.     

Thermodynamics of metal ion binding. 2. Metal ion binding by carbonic anhydrase variants

The ability to construct molecular motifs with predictable properties in aqueous solution requires an extensive knowledge of the relationships between structure and energetics. The design of metal binding motifs is currently an area of intense interest in the bioorganic community. To date synthetic motifs designed to bind metal ions lack the remarkable affinities observed in biological systems. To better understand the structural basis of metal ion affinity, we report here the thermodynamics of binding of divalent zinc ions to wild-type and mutant carbonic anhydrases and the interpretation of these parameters in terms of structure. Mutations were made both to the direct His ligand at position 94 and to indirect, or second-shell, ligands Gln-92, Glu-117, and Thr-199. The thermodynamics of ligand binding by several mutant proteins is complicated by the development of a second zinc binding site on mutation; such effects must be considered carefully in the interpretation of thermodynamic data. In all instances modification of the protein produces a complex series of changes in both the enthalpy and entropy of ligand binding. In most cases these effects are most readily rationalized in terms of ligand and protein desolvation, rather than in terms of changes in the direct interactions of ligand and protein. Alteration of second-shell ligands, thought to function primarily by orienting the direct ligands, produces profoundly different effects on the enthalpy of binding, depending on the nature of the residue. These results suggest a range of activities for these ligands, contributing both enthalpic and entropic effects to the overall thermodynamics of binding. Together, our results demonstrate the importance of understanding relationships between structure and hydration in the construction of novel ligands and biological polymers.     

Immobilization of Chacoan peccaries (Catagonus wagneri) using medetomidine, Telazol, and ketamine

A combination of medetomidine, Telazol, and ketamine hydrochloride was used to immobilize captive Chacoan peccaries (Catagonus wagneri) for translocation within Paraguay during August-October 2002. Animals were darted in enclosed areas of varying size. The average dose used was 32.5+/-7.2 microg/kg of medetomidine, 0.63+/-0.2 mg/kg of Telazol, and 3.9+/-0.65 mg/kg of ketamine. First effects were noted at 4.3+/-2.1 min, and ability to handle the animals was achieved by 12.6+/-3.7 min. Heart and respiratory rates declined and oxygen saturation increased during anesthesia. Muscle relaxation was good. Atipamezole was used to antagonize the medetomidine, although recoveries were still slow. This drug combination provided adequate immobilization of Chacoan peccaries; however, this protocol would not be considered to be reversible, and confinement during recovery is recommended.     

Cloning, isolation and characterization of the Thermotoga maritima KDPG aldolase

The Thermotoga maritima aldolase gene has been cloned into a T7 expression vector and overexpressed in Escherichia coli. The preparation yields 470 UL(-1) of enzyme at a specific activity of 9.4 U mg(-1). During retroaldol cleavage of KDPG, the enzyme shows a k(cat) that decreases with decreasing temperature. A more than offsetting decrease in K(m) yields an enzyme that is more efficient at 40 degrees C than at 70 degrees C. The substrate specificity of the enzyme was evaluated in the synthetic direction with a range of aldehyde substrates. Although the protein shows considerable structural homology to KDPG aldolases from mesophilic sources, significant differences in substrate specificity exist. A preparative scale reaction between 2-pyridine carboxaldehyde and pyruvate provided product of the same absolute configuration as mesophilic enzymes, but with diminished stereoselectivity.     

Biodiversity associated with restored small-scale mussel habitats has restoration decision implications

The global loss of marine ecosystem engineers has caused an unprecedented decline in biodiversity. Although wild shellfish habitats have been shown to support biodiverse ecosystems, little is known about how biodiversity is altered by restored shellfish habitats, particularly mussels. To explore the biodiversity response to restored mussel habitats we deposited mussels on the seafloor in 1.5?×?1.5 m plots across a gradient of benthic environments. To understand a holistic community response, this study looks at the response of three faunal classifications over 1 year: infauna, epifauna, and pelagic fauna, compared with adjacent control plots (no mussels). The restored mussel habitats recorded 42 times more demersal fish than control areas, while macroalgae and mobile benthic invertebrates had over a twofold increase in abundance. Overall, the addition of mussels to the seafloor resulted in a general reduction of infaunal abundance and biodiversity, but an increase in epifaunal and pelagic faunal abundances, specifically from those species that benefit from benthic habitat complexity and an increase in food availability. From a management perspective, we highlight location-specific differences to consider for future restoration efforts, including environmental conditions and potential observed factors such as nearby sources of species, particularly predators, and relevant demersal fish ranges. Ultimately, measuring biodiversity responses in small-scale studies will serve as a valuable guide for larger scale restoration efforts and this study recommends considerations to enhance biodiversity outcomes in restored mussel habitats.

     

Directed evolution of a pyruvate aldolase to recognize a long chain acyl substrate

The use of biological catalysts for industrial scale synthetic chemistry is highly attractive, given their cost effectiveness, high specificity that obviates the need for protecting group chemistry, and the environmentally benign nature of enzymatic procedures. Here we evolve the naturally occurring 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolases from Thermatoga maritima and Escherichia coli, into enzymes that recognize a nonfunctionalized electrophilic substrate, 2-keto-4-hydroxyoctonoate (KHO). Using an in vivo selection based on pyruvate auxotrophy, mutations were identified that lower the K(M) value up to 100-fold in E. coli KDPG aldolase, and that enhance the efficiency of retro-aldol cleavage of KHO by increasing the value of k(cat)/K(M) up to 25-fold in T. maritima KDPG aldolase. These data indicate that numerous mutations distal from the active site contribute to enhanced 'uniform binding' of the substrates, which is the first step in the evolution of novel catalytic activity.