Irreversible transformations of native celluloses, upon exposure to elevated temperatures.

Current research, basic and applied, assumes that observed recalcitrance of celluloses is an inherent characteristic associated with their state of aggregation in their native state; it is thought that processes of isolation remove other components of plant cell walls leaving the celluloses unchanged, even though elevated temperatures are routinely used during isolation. Since temperature elevation is known to influence the structures of all polymers, it is important to explore its influence on the character of isolated celluloses, almost always assumed to be still in their native state. Deuterium exchange is a measure of accessibility of reactive sites in celluloses. We report significant reduction in accessibility to deuterium and other probe molecules for celluloses isolated at ambient temperature and then exposed to elevated temperatures. Our results indicate that native celluloses, which are highly ordered biological structures, are irreversibly transformed and develop polymeric semi-crystalline character upon isolation at elevated temperatures.

Modeling of the metallo-beta-lactamase from B. fragilis: structural and dynamic effects of inhibitor binding.

The structure and dynamics of an inhibitor-bound complex of the metallo-beta-lactamase from Bacteroides fragilis are studied by using molecular dynamics. A search of the conformational space was performed to obtain three distinct models of the complex, which were then subjected to solvated molecular dynamics. A solvated molecular dynamics study of the apo protein was performed to serve as a baseline for comparison with the bound simulations. We find loop conformation changes due to binding as well as a decrease in flexibility of the protein as a whole and especially in the major loop of the beta-lactamase. We report the structural and dynamical features of the inhibitor-bound and apo models, as well as experimentally measurable quantities, which should be capable of distinguishing the two binding modes we have determined.

A molecular level picture of the stabilization of A-DNA in mixed ethanol-water solutions.

Advances in computer power, methodology, and empirical force fields now allow routine "stable" nanosecond-length molecular dynamics simulations of DNA in water. The accurate representation of environmental influences on structure remains a major, unresolved issue. In contrast to simulations of A-DNA in water (where an A-DNA to B-DNA transition is observed) and in pure ethanol (where disruption of the structure is observed), A-DNA in approximately 85% ethanol solution remains in a canonical A-DNA geometry as expected. The stabilization of A-DNA by ethanol is likely due to disruption of the spine of hydration in the minor groove and the presence of ion-mediated interhelical bonds and extensive hydration across the major groove.

Evaluation of a serum/plasma separator: suitability of samples for radioimmunoassay and competitive protein binding techniques.

A new method of separating serum or plasma from whole blood (Sure-Sep, W.R. Warner) has been evaluated with particular regard to the suitability of the serum/plasma samples for radioimmunoassay (R.I.A.) and competitive protein binding (C.P.B.) techniques. Sure-Sep did not affect the results obtained for the following assays: cortisol, thyroxine, triidothyronine, insulin, and growth hormone. In addition it was also found that contact of the serum or plasma samples with Sure-Sep for 24 hours at 4 degrees C was without effect on the results obtained.

Is glucagon important in stable insulin-dependent diabetics?

The role of glucagon has been evaluated in the everyday regulation of carbohydrate and lipid metabolism in insulin-dependent diabetic patients. Plasma concentrations of glucagon, growth hormone, cortisol, glucose, and free fatty acids and blood concentrations of glycerol, 3-hydroxybutyrate, acetoacetate, alanine, pyruvate, and lactate were measured in 38 fasting diabetic subjects deprived of their usual morning dose of insulin. The measurements were repeated in 25 of these patients after a further 3 hours of insulin deprivation and in 6 patients again at 6 hours. There was no correlation between the initial fasting levels of plasma-glucagon and those of the other biochemical measurements including glucose and ketone bodies. Furthermore, no correlation was found between changes in these measurements and in plasma-glucagon over a period of 3 or 6 hours. These findings suggest that glucagon is unlikely to play a role of primary importance in blood-glucose homoeostasis or ketone-body metabolism in ambulant insulin-dependent diabetic patients.

Assessment of a simple competitive protein-binding technique for plasma cortisol assay.

The Cortipac kit for cortisol assay by a competitive protein-binding technique (CPB) which utilizes 75Se cortisol has been evaluated. Results obtained by it agree well with those by the Mattingly fluorimetric method. Assays can be carried out on either plasma or serum and haemolysis does not interfere. The specificity of the assay was checked in blood samples from patients receiving synthetic steroids. Prednisone and prednisolone therapy caused significant interference with the assay; fluorocortisol and dexamethasone therapy did not. The increased progesterone in late pregnancy blood samples had only a small effect on the assay. Plasma samples for cortisol assay could be stored for at least 4 weeks at 4 degrees C and for at least 12 weeks at -20 degrees C.