Species loss and aboveground carbon storage in a tropical forest

Tropical forest biodiversity is declining, but the resulting effects on key ecosystem services, such as carbon storage and sequestration, remain unknown. We assessed the influence of the loss of tropical tree species on carbon storage by simulating 18 possible extinction scenarios within a well-studied 50-hectare tropical forest plot in Panama, which contains 227 tree species. Among extinction scenarios, aboveground carbon stocks varied by more than 600%, and biological insurance varied by more than 400%. These results indicate that future carbon storage in tropical forests will be influenced strongly by future species composition.     

Evidence for interstitial carbon in nitrogenase FeMo cofactor

The identity of the interstitial light atom in the center of the FeMo cofactor of nitrogenase has been enigmatic since its discovery. Atomic-resolution x-ray diffraction data and an electron spin echo envelope modulation (ESEEM) analysis now provide direct evidence that the ligand is a carbon species.     

Phenol oxidases of a lozenge mutant of Drosophila

Monophenol oxidase (or tyrosinase-A(1)) activity appears to be absent from extracts from pupae of homozygous lozenge-glossy (lz(g)/lz(g)) females and (lz(g)/male symbol) males of Drosophila melanogaster. Diphenol oxidase (tyrosinase-A(2)) activity is less in the mutant extracts than in extracts of wild-type Oregon-R pupae of the same age and sex.     

Tales from a troubled marriage: science and law in environmental policy

Early environmental policy depended on science, with mixed results. Newer approaches continue to rely on science to identify problems and solve them, but use other mechanisms to set standards and legal obligations. Given the important role that science continues to play, however, several cautionary tales are in order concerning "scientific management," "good science," the lure of money, and the tension between objectivity and involvement in important issues of our time.     

Nucleotide control of interdomain interactions in the conformational reaction cycle of SecA

The SecA adenosine triphosphatase (ATPase) mediates extrusion of the amino termini of secreted proteins from the eubacterial cytosol based on cycles of reversible binding to the SecYEG translocon. We have determined the crystal structure of SecA with and without magnesium-adenosine diphosphate bound to the high-affinity ATPase site at 3.0 and 2.7 angstrom resolution, respectively. Candidate sites for preprotein binding are located on a surface containing the SecA epitopes exposed to the periplasm upon binding to SecYEG and are thus positioned to deliver preprotein to SecYEG. Comparisons with structurally related ATPases, including superfamily I and II ATP-dependent helicases, suggest that the interaction geometry of the tandem motor domains in SecA is modulated by nucleotide binding, which is shown by fluorescence anisotropy experiments to reverse an endothermic domain-dissociation reaction hypothesized to gate binding to SecYEG.