Site-directed paramagnetic nitroxide radicals (spin labels) have been used to perturb the nuclear magnetic resonance spectra of specific protons in lysozyme and in bound inhibitors. The broadening of nuclear resonance lines has been used to calculate distances of up to 20 A between the nitroxide radical electron and protons of interest. Lysozyme covalently

The nuclear magnetic resonance (NMR) of water protons in live and glycerinated muscle, suspensions of glycerinated myofibrils, and solutions of several muscle proteins has been studied. T(1) and T(2), measured on partially hydrated proteins by pulsed spin-echo techniques, decreased as the ratio of water to protein decreased, showing that the water which is tightly bound by the protein has short relaxation times. In live muscle fibers the pulse techniques showed that, after either a 180 or a 90 degrees pulse, the relaxation of the magnetization is described by a single exponential. This is direct evidence that a fast exchange of protons occurs among the phases of the intracellular water. The data can be fitted with a model in which the bulk of the muscle water is in a phase which has properties similar to those of a dilute salt solution, while less than 4-5% of the total water is bound to the protein surface and has short relaxation times. Measurements of T(1) and T(2) in protein solutions showed that no change in the proton relaxation times occurred when heavy meromyosin was bound to actin, when myofibrils were contracted with adenosine triphosphate (ATP), or when globular actin was polymerized.

Prescission (v;") and postscission (est) neutron multiplicities have been measured for the reactions p+"' ' ' "U at several projectile energies between 12.7 and 25.6 MeV in coincidence with binary fragments. Separation of v;" from v~t was achieved under the assumption of isotropic emission in the respective source frames. Both multiplicities increase with initial excitation energy Ec" with comparable rates EECN/hv=17+3 MeV. v;"(E~N) extends existing data of heavy-ion induced fusion-fission with ECN 50 MeV; for EcN~2 0 MeV it is incompatible with the transitionstate model and cannot be reproduced without a delay time for the fission competition in the order of 3X10 -10 ' s. The fragment mass dependence v~"(m) shows a clear sawtooth structure for all three targets at E~= 12.6 MeV that is gradually washed out with increasing E~o r decreasing total kinetic energy TKE, because the heavier fragment receives most of the additional excitation energy. The nuclear temperatures of the heavy fragments exceed those of the light ones, but seem to approach each other with increasing fragment excitation. sa et al. " predicts the structure to persist with growing ECN (but shifted upward in absolute number}, whereas the statistical scission point model' does not. At present, there are three classes of theoretical approaches to the fission process in discussion. The statistical model of Wilkins et al. ' assumes a quasistability at the scission point. It can be applied to all kinds of nuclear fission, in particular those with high mass asymmetry and those which are strongly influenced by shell effects, but it has its problems' with the widths of the fragment mass distributions. The liquid drop model is essentially restricted to symmetric fission' and therefore not very appropriate for the reaction systems under discussion. Recently, Brosa et al. ' introduced a model based on a random neck rupture that naturally leads to the experimentally observed widths of mass distributions and predicts the sawtooth v"", (m) as a consequence of 41

No abstract