Cross-Coupling of Mo- and V-Nitrogenases Permits Protein-Mediated Protection from Oxygen Deactivation.

Nitrogenases catalyze dinitrogen (N) fixation to ammonia (NH). While these enzymes are highly sensitive to deactivation by molecular oxygen (O) they can be produced by obligate aerobes for diazotrophy, necessitating a mechanism by which nitrogenase can be protected from deactivation. In the bacterium Azotobacter vinelandii, one mode of such protection involves an O-responsive ferredoxin-type protein ("Shethna protein II", or "FeSII") which is thought to bind with Mo-dependent nitrogenase's two component proteins (NifH and NifDK) to form a catalytically stalled yet O-tolerant tripartite protein complex.

The Mononuclear Metal-Binding Site of Mo-Nitrogenase Is Not Required for Activity.

The biological N-fixation process is catalyzed exclusively by metallocofactor-containing nitrogenases. Structural and spectroscopic studies highlighted the presence of an additional mononuclear metal-binding (MMB) site, which can coordinate Fe in addition to the two metallocofactors required for the reaction. This MMB site is located 15-Å from the active site, at the interface of two NifK subunits.

Nitrogen Fixation and Hydrogen Evolution by Sterically Encumbered Mo-Nitrogenase.

The substrate-reducing proteins of all nitrogenases (MoFe, VFe, and FeFe) are organized as αß(γ) multimers with two functional halves. While their dimeric organization could afford improved structural stability of nitrogenases , previous research has proposed both negative and positive cooperativity contributions with respect to enzymatic activity. Here, a 1.

Evaluation of pediatric lateral oropharyngeal trauma.

Objective: We reviewed the mechanism of injury, presentation, and evaluation of children with trauma to the lateral oropharynx. Study design and setting We conducted a retrospective review of patients in an urban pediatric emergency department with trauma to the lateral oropharynx over a 5-year period.

Results: Forty-eight patients were identified with documented injuries of the lateral oropharynx placing the internal carotid artery at risk of injury.