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The biomass and primary productivity of phytoplankton assemblages from the marginal ice zone of the Fram Strait were investigated during June-July 1984 as part of the 1984 Marginal Ice Zone Experiment. The entire region was characterized by strong vertical stratification and reduced nutrient concentrations near the surface. Chlorophyll a levels were elevated at the ice edge and decreased both under the ice and away from the ice edge. Chlorophyll concentrations were greatest at the top of the pycnocline and averaged 2.9 #g L-• at 20 m. Primary productivity was also greatest at the ice edge, with daily integrated productivity averaging 426 mg C m -2 d -•. Small flagellates numerically dominated the assemblages. Growth rates, when corrected for detrital material, were close to their potential maximum for the temperatures encountered. Large differences between the water temperatures, nitrate concentrations, and chlorophyll a levels during similar periods in 1983 and 1984 were noted. These differences, in addition to the spatial and temporal variations in biological processes induced by mesoscale eddies, suggest that the interannual variability in marginal ice zones may have significant consequences to the region's food web dynamics.

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Carbonic anhydrase (CA) is a well-studied, zinc-dependent metalloenzyme that catalyzes the hydrolysis of carbon dioxide to the bicarbonate ion. The apo-form of CA (apoCA) is relatively easy to generate, and the reconstitution of the human erythrocyte CA has been initially investigated. In the past, these studies have continually relied on equilibrium dialysis measurements to ascertain an extremely strong association constant (Ka ~ 1.2×1012) for Zn2+. However, new reactivity data and isothermal titration calorimetry (ITC) data reported herein call that number into question. As shown in the ITC experiments, the catalytic site binds a stoichiometric quantity of Zn2+ with a strong equilibrium constant (Ka ~ 2 × 109) that is three orders of magnitude lower than the previously established value. The thermodynamic parameters associated with Zn2+ binding to apoCA are unraveled from a series of complex equilibria associated with the in vitro metal binding event. This in-depth analysis adds clarity to the complex ion chemistry associated with zinc binding to carbonic anhydrase and validates thermochemical methods that accurately measure association constants and thermodynamic parameters for complex-ion and coordination chemistry observed in vitro. Additionally, the zinc sites in both the as-isolated and reconstituted ZnCA were probed using X-ray absorption spectroscopy. Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses indicate the zinc center in the reconstituted carbonic anhydrase is nearly identical to that of the as-isolated protein and confirms the notion that the metal binding data reported herein is the reconstitution of the zinc active site of human CA II.

Latent M. tuberculosis infection presents one of the major obstacles in the global eradication of tuberculosis (TB). Cholesterol plays a critical role in the persistence of M. tuberculosis within the macrophage during latent infection. Catabolism of cholesterol contributes to the pool of propionyl-CoA, a precursor that is incorporated into cell-wall lipids. Arylamine N-acetyltransferase (NAT) is encoded within a gene cluster that is involved in the cholesterol sterol-ring degradation and is essential for intracellular survival. The ability of the NAT from M. tuberculosis (TBNAT) to utilise propionyl-CoA links it to the cholesterol-catabolism pathway. Deleting the nat gene or inhibiting the NAT enzyme prevents intracellular survival and results in depletion of cell-wall lipids. TBNAT has been investigated as a potential target for TB therapies. From a previous high-throughput screen, 3-benzoyl-4-phenyl-1-methylpiperidinol was identified as a selective inhibitor of prokaryotic NAT that exhibited antimycobacterial activity. The compound resulted in time-dependent irreversible inhibition of the NAT activity when tested against NAT from M. marinum (MMNAT). To further evaluate the antimycobacterial activity and the NAT inhibition of this compound, four piperidinol analogues were tested. All five compounds exert potent antimycobacterial activity against M. tuberculosis with MIC values of 2.3–16.9 µM. Treatment of the MMNAT enzyme with this set of inhibitors resulted in an irreversible time-dependent inhibition of NAT activity. Here we investigate the mechanism of NAT inhibition by studying protein-ligand interactions using mass spectrometry in combination with enzyme analysis and structure determination. We propose a covalent mechanism of NAT inhibition that involves the formation of a reactive intermediate and selective cysteine residue modification. These piperidinols present a unique class of antimycobacterial compounds that have a novel mode of action different from known anti-tubercular drugs.