Signe Andersen

Determination of reserve albumin-equivalent for ligand binding, probing two distinct binding functions of the protein

Abstract A method is reported for determination of albumin binding capacity for various ligands in 50-μl sample volumes. A small amount of a radioactively labeled test ligand is added to the undiluted sample and the rate of dialysis of the free ligand into an identical sample without added ligand is measured. The reserve albumin-equivalent concentration is defined as the concentration of a standard albumin preparation which in buffered solution gives the same rate of dialysis and hence the same ratio of free/bound concentrations of the added ligand. It is shown that the reserve albumin-equivalent concentration, thus defined, is identical with the sum of concentrations of carrier species, each multiplied by the first stoichiometric binding constant of the test ligand to the carrier and divided by its first stoichiometric binding constant to the standard albumin. Determinations of this parameter are suitable for studies of the chemical potential and transfer affinities of individual ligands and for determination of interaction among several binding substances. Two test ligands have been used, monoacetyldiaminodiphenyl sulfone and diazepam. The former is bound competitively with bilirubin while diazepam engages another, independent binding function. The method can thus be used for separate determinations of the degree of saturation of two distinct binding functions of albumin. Complex mixtures of several carrier proteins with interacting ligands can be studied.

Status of the harbour seal ( Phoca vitulina ) in Southern Scandinavia

The harbour seal population in Southern Scandinavia has experienced repeated declines caused by hunting and epizootics. These events have shaped the current distribution and abundance of the population. This paper assesses the current status of the population. We estimate trends in abundance of harbour seals from long term survey data, compare these with historic trends inferred from previously published material, and discuss past and potential threats to the harbour seal population of Southern Scandinavia. It is evident that harbour seals have disappeared from haulout areas along the Danish shores of Kattegat and in the westernmost part of the Baltic Sea, where they were previously numerous. In the 1920-30s, when abundance was at its lowest, the population is estimated to have been only a fraction of its original size. Following 30 years of protection the population is currently approaching historic abundance and might have reached the carrying capacity in some areas. Further development depends largely on effects of future epizootics, anthropogenic disturbance, and availability of suitable haulout sites.

Valproate competes with palmitate for binding to serum albumin

Summary: Addition of sodium valproate (VPA) to a buffered solution of human serum albumin (HSA) or to serum reduces binding affinity for palmitate. A maximal pharmacologic VPA concentration, 700 μM added to a 300‐μM albumin solution, reduces the reserve albumin concentration for binding of palmitate by a factor of 0.64. One possible site model explaining these findings may be that VPA competes strongly with one among three palmitate molecules, bound to albumin with high affinity, and induces a weaker displacement of a second palmitate.

Measurement of palmitate availability in serum samples: method and utility

Palmitic acid shows a very low and unknown solubility at neutral pH. Binding equilibria of palmitate to human serum albumin accordingly cannot be investigated by measuring free and bound ligand concentrations as in conventional binding studies. It is feasible, on the other hand, to describe the binding equilibria in relative terms, by measuring the concentration, p, of reserve albumin, previously defined as the concentration of a purified standard albumin preparation which in buffered solution binds a trace amount of palmitate as tight as it is bound in the sample. Palmitate availability is calculated as C/p, when C is the concentration of bound palmitate. The general binding equation is modified to contain the availability beside relative binding constants, Li = Ki/K1,St, where K1,St is the first stoichiometric binding constant for palmitate to the standard albumin preparation. Availabilities and relative binding constants can replace free concentrations and usual binding constants in considerations of biochemical transport and enzymatic mechanisms. A method is described for measuring the concentration of reserve albumin for binding of palmitate, based upon determination of dialytic exchange rates for palmitate among identical equilibrium samples. A technique for reproducibly adding radiolabelled palmitate to the samples is given.