Aspects of the dosimetry of plutonium in bone.

After animals have been exposed to plutonium it eventually becomes distributed unevenly throughout the bone tissue. There is therefore a need to study the dosimetry of plutonium, particularly 239Pu, as a function of its depth of burial in bone. This article discusses a simple approach to the problem, and the magnitude of some of the possible errors involved.     

Peculiar dynamical properties of plutonium hydrides

In the present work, the structure and spectra of PuH and PuH₂ are defined by B3LYP/SDD method, from which the analytic potential energy function of PuH₂ is derived. The analysis of quasi-classical molecular reaction dynamics is performed to study the state-state process of Pu(⁷F_g)+H₂(X¹Σ⁺_g). It is found that the reaction Pu(⁷F_g)+H₂(X¹Σ⁺_g)→PuH₂(X⁷B₁) has no threshold. The simultaneous hydrogenation process of plutonium with the main product of PuH₂ is theoretically proved for the first time.     

Binding of disease-associated prion protein to plasminogen

Transmissible spongiform encephalopathies are associated with accumulation of PrP(Sc), a conformer of a cellular protein called PrP(C). PrP(Sc) is thought to replicate by imparting its conformation onto PrP(C) (ref. 1), yet conformational discrimination between PrP(C) and PrP(Sc) has remained elusive. Because deposition of PrP(Sc) alone is not enough to cause neuropathology, PrP(Sc) probably damages the brain by interacting with other cellular constituents. Here we find activities in human and mouse blood which bind PrP(Sc) and prion infectivity, but not PrP(C). We identify plasminogen, a pro-protease implicated in neuronal excitotoxicity, as a PrP(Sc)-binding protein. Binding is abolished if the conformation of PrP(Sc) is disrupted by 6M urea or guanidine. The isolated lysine binding site 1 of plasminogen (kringles I-III) retains this binding activity, and binding can be competed for with lysine. Therefore, plasminogen represents the first endogenous factor discriminating between normal and pathological prion protein. This unexpected property may be exploited for diagnostic purposes.     

Binding of myosin I to membrane lipids

The single-headed myosins called myosin-I were first isolated from the protozoan Acanthamoeba and subsequently identified in other cells. We previously reported evidence that myosin-I is responsible for the movement of membranes, extracted from Acanthamoeba, along actin filaments in vitro. Here we show for the first time that myosin-I can bind directly to NaOH-extracted membranes isolated from Acanthamoeba and to vesicles of pure lipids with an affinity sufficient for extensive binding in the cell. Membrane-bound myosin-I may provide a mechanism for many cellular movements previously thought to involve filamentous myosin-II.