The empirical diclectric decay function y ( t ) -= exp -( f / ~~) p may be transformed analytically to give the frequency dependent complex dielectric constant if p is chosen to be 0.50. The resulting dielectric constant and dielectric loss curves are non-symmetrical about the logarithm of the frequency of maximum loss, and are intermediate between the Cole-Cole and Davidson-Cole empirical relations.Using a short extrapolation procedure, good agreement is obtained between the empirical representation and the experimental curves for the a relaxation in polyethyl acrylate. It is suggested that the present representation would have a general application to the a relaxations in other polymers.

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1. The substrate combination creatine-MgADP does not significantly protect creatine kinase against inhibition by iodoacetamide in the absence of small anions. 2. Small anions can be divided into three groups according to the way in which they affect creatine kinase: I, acetate reversibly increases enzyme activity in the forward reaction but does not affect the rate of inhibition by iodoacetamide in the presence of creatine plus MgADP; II, planar anions and some halides (HCO(3) (-), HCO(2) (-), NO(3) (-), NO(2) (-), Cl(-), Br(-), F(-)) in the presence of creatine plus MgADP protect the enzyme from inhibition by iodoacetamide; III, tetrahedral anions (SO(4) (2-), HPO(4) (2-), ClO(4) (-), BF(4) (-)) and iodide do not affect the rate of inhibition by iodoacetamide in the presence of creatine plus MgADP but may decrease the protection by class II anions under these conditions. Anions of class II and class III also reversibly inhibit enzyme activity. 3. It is concluded that class II anions form a stable and inactive quaternary enzyme-creatine-MgADP-anion complex and this is responsible for the effect attributed by previous workers to the ternary complex lacking anion. Formation of this complex, particularly in the forward reaction, can lead to markedly non-linear enzyme progress curves. Some previous observations are re-appraised in the light of these findings. 4. From the behaviour of chloride and nitrate ions, and the marked lowering of the K(i) values for creatine and MgADP they produce, it is inferred that planar or monoatomic anions act in the quaternary complex by simulating the transferable phosphoryl group in the transition state (or another intermediate state) of the reaction. 5. It is suggested that, in the course of the reaction, the tetrahedral phosphate-binding site for the transferable phosphoryl group of the substrate (that also binds class II and class III anions) changes into a trigonal bipyramid site (also occupied by class II anions). This strains the phosphoryl group to adopt the transitional sp(3)d hybridized state and must contribute significantly to the low activation energy of the reaction. 6. Catalysis is deduced to proceed by an ;in line' transfer reaction and from the effects of class II anions it is possible to estimate the approximate dimensions of the anionic site in the transition-state complex. 7. The specific protecting effect of an equilibrium mixture of substrates against inhibition by iodoacetamide provides further evidence for the conformational change suggested above as a step in the catalytic process.

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The aim of this investigation was to compare two methods of assessing the surface texture of finished dental ceramic; a laser reflectivity method (LSR) and a contact stylus tracing method. Identical ceramic blocks (Dicor MGC) were finished using a variety of techniques and devices, and the surface texture characterized by LSR and contact stylus tracing to enable comparisons to be made between the two methods. The results indicate that there is little correlation between the two measuring methods. Therefore, laser reflectivity should not be exclusively used to measure the surface texture of contoured and finished ceramic materials. The development of sophisticated surface characterization parameters suggest that the surface characteristics of dental restorations and other related surfaces should be described using more than one surface measurement parameter. Surface parameters should be chosen which can both quantify surface roughness and provide information on the shape of the surface under investigation.

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