A comparative study of some physico-chemical properties of human serum albumin samples from different sources--II. The characteristics of the N-B transition and the binding behaviour with regard to warfarin and diazepam.

A comparative study of the N-B transition and the drug binding properties of human serum albumin samples from various sources has been carried out with the help of circular dichroism and equilibrium dialysis. It was found that when warfarin was used as a marker the midpoint pH and the cooperative nature of the N-B transition that occurs in the albumin around physiological pH varied with the albumin sample. The midpoint pH was found to be related to the cooperative nature of the albumin samples. A similar relationship has been found for allosteric proteins. However, when diazepam was used as a marker molecule for the N-B transition, variations in the midpoint pH and cooperative nature of the N-B transition disappeared. This is attributed to the strong allosteric effect of diazepam on binding. The affinity of warfarin for albumin depends strongly on the sample, but this is not the case with diazepam. The cooperative binding properties found for the albumin samples are compared with those found for the albumin in serum. After a discussion it is concluded that the cooperative binding properties of a particular albumin sample should be taken into account when that sample is used in binding studies.