A water sluice is generated in the active site of bovine lens leucine aminopeptidase

Nature has provided the binuclear zinc based active site of bovine lens leucine aminopeptidase (blLAP) with two water channels: one for substrate docking and a much smaller one (function unknown) above Zn1. In addition, Zn1 possesses an unusual pentacoordinate geometry with a loosely bound carbonyl ligand (Ala333). Extensive DFT calculations on a model of the active site provide first mechanistic implications for these structural features. The weakly bound carbonyl ligand is capable of functioning as a "traffic cop" to direct water molecules coming from the small channel into the heart of the active site. A water sluice is thus generated that is capable of repeatedly providing a series of nucleophilic active "Zn-OH" functionalities.     

New Insight into the Mode of Action of Nickel Superoxide Dismutase by Investigating Metallopeptide Substrate Models

For the first time, the existence of a substrate adduct of a nickel superoxide dismutase (NiSOD) model, based on the first nine residues from the N terminus of the active form of Streptomyces coelicolor NiSOD, has been proven and the adduct has been isolated. This adduct is based on the cyanide anion (CN^?), as a substrate analogue of the superoxide anion (O₂^.?), and the nickel metallopeptide H‐HCDLPCGVY‐NH₂‐Ni. Spectroscopic studies, including IR, UV/Vis, and liquid‐ and solid‐state NMR spectroscopy, show a single nickel‐bound cyanide anion, which is embedded in the metallopeptide structure. This complex sheds new light on the question of whether the mode of action of the NiSOD enzyme is an inner‐ or outer‐sphere mechanism. Whereas discussion was previously biased in favor of an outer‐sphere electron‐transfer mechanism due to the fact that binding of cyanide or azide moieties to the nickel active site had never been observed, our results are a clear indication in favor of the inner‐sphere electron‐transfer mechanism for the disproportionation of the O₂^.? ion, whereby the substrate is attached to the Ni atom in the active site of the NiSOD.     

Efforts to Foster All-Channel Television

The Federal Communications Commission (FCC) has long considered 12 VHF channels incapable of providing an efficient television system. Its responsibilities to make UHF broadcasting competitive with VHF led it to seek authority from Congress to require that all receivers be equipped with UHF tuners. Having obtained this authority, the FCC turned to other concurrent activities which would lead to surmounting the technical and nonechnical problems encountered in UHF broadcasting. In particular, an industry advisory committee was formed in 1963 entitled, "Committee for the Full Development of All-Channel Broadcasting." This Committee makes recommendations to the FCC as to how, by amendment of its rules and policies, UHF broadcasting can become fully viable.     

Theory of absorbers in scattering

The effect of absorbers on scattering from complex shapes is considered, wherein, unlike previous work on the subject, the diffracted field is taken into account. For a general class of scattering bodies two new theorems are introduced which give conditions under which the back-scattered field for incident radiation is identically zero. High-frequency scattering from any smooth convex body is examined. The conditions given in the theorems are then used to determine their effect on the creeping waves. It is shown that the creeping waves suffer much greater attenuation than they would if the body were a perfectly conducting surface. The particular case for nose-on back-scattering from a body of revolution is considered, for which case the creeping wave contribution to the back-scattered field is identically zero due to phase cancellation. It is then shown that absorbers with highly refractive lossy characteristics will reduce the back-scattered cross section for smooth convex bodies in the resonance region.     

Aminoboranes: Their use in the synthesis of sulphenamides

Sulphenamides have been prepared in good yields and under mild conditions from the reaction of an aminoborane with a sulphenic ester.