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The adiabatic compressibility of several globular proteins has been measured by using an ultrasonic technique in the frequency range 0.5 to 10 MHz. The contributions to the measured compressibility from the protein matrix and from surface processes involving ionization of side chains and solvation effects are discussed. The internal protein compressibility is very low, indicating the existence of "dynamic domains" which are tentatively assigned to secondary structure elements.

Analysis of the plethysmographic pulse volume contour in terms of "crest time", made in 1940-1960, revealed age dependence and clinically significant variations between health and disease, including arteriosclerosis, hypertension and various dermatoses. A new parameter--"minimum rise-time" (MRT) is suggested and defined from pulse volume contour. In health it was found to be age dependent using finger photoplethysmography. The MRT of the pulse volume is shown by a model 1) to be associated with the mechanical properties (viscoelasticity) of the vascular wall, 2) to approximate the MRT of the pulse pressure, and 3) to be free of ambiguities found in "crest time" and "half rise-time" previously used. The analysis suggests that the gradient of the MRT along peripheral vessels might be a clinical indication of variations in the mechanical properties of the vascular wall.

This paper considers the multidimensional weighted minimax location problem, namely, finding a facility location that minimizes the maximal weighted distance to n points. General distance norms are used. An epsilon-approximate solution is obtained by applying a variant of the Russian method for the solution of Linear Programming. The algorithm has a time complexity of O(n log epsilon) for fixed dimensionality k. Computational results are presented.

Recent x-ray studies of metmyoglobin at different temperatures [Frauenfelder, H. Petsko, G. A. & Tsernoglou, D. (1979) Nature (London) 280, 558-563] show that the dependence of the mean square displacements of individual atoms on the absolute temperature T can be described analytically by T mu, in which the parameter mu undergoes local variations in the range -2 to +20. This strong deviation from harmonic behavior mu = 1 is modelled here, in the classical limit, by local nonharmonic potentials, in which a particle spends part of its time in one or more weakly bound states (traps) and the rest of it as an almost free particle in a restricted volume (cavity). Analytic calculations of the mean square atomic displacement in such cavity--traps potentials for a simplified three-dimensional geometry yield the following results: A parametrically described T mu behavior characterizes a transition region in temperature below which the particle is "trapped" (solid-like) and above which the particle is "free" (liquid-like). The magnitude of mu increases with an increase in the ratio of cavity volume to trap volume. Mu greater than 0 type of behavior can be obtained by a single trap and mu less than 0 by two symmetric traps. A comparison is made between the predictions of the model and the experimental results, and the elucidation of the model parameters from x-ray data is discussed.

A theory is developed, where a linear macromolecule with geometrically constrained ends, elastically strained, exchanging energy with the solvent molecules through random collisions may provide a mechanism for the following specific functions in proteins: a) Induction of transient, oriented strains in substrates during transition between conformations. b) External variation of the rigidity and geometry of the active site. More generally, a macromolecule in solution possessing appropriate geometrical and elastic properties constitutes a machine, whose possible operations have common features with biological function such as passive transport, enzymatic catalysis and active transport. The theory suggests a quantitative law by which new information about the dynamical state of the protein molecule can be elucidated from the Arrhenius plot. It predicts a relationship between the rate of catalysis and the local viscosity of the solution.