Study of human serum albumin structure by dynamic light scattering: two types of reactions under different pH and interaction with physiologically active compounds.

The effect of pH and binding of ten physiologically active compounds (isoproterenol, yohimbine, propranolol, clonidine, phenylephrine, carbachol, tripeptide fMLP, diphenhydramine, chlorpromazine and atropine) on the molecular structure of human serum albumin (HSA) has been studied using the dynamic light scattering. It was found that albumin globule has the most compact configuration (Stokes diameter 59-62 A) at physiological pH 7.4. The changes in pH, both increase to 8.0 and decrease to 5.4, result in the growth of globule size to 72-81 A. At acidic shift of pH an additional peak arises in the correlation spectra caused by the light scattering on the structures with the Stokes diameters of 29-37 A. Those conform to the sizes of the albumin subdomains. The indicated peak is not displayed at basic shift of pH. The interaction with propranolol, clonidine, phenylephrine, carbachol and tripeptide fMLP which hinder adenylate cyclase (AdC) and activate Ca-polyphosphoinositide (Ca-PPI) signaling system of a cell initiates structural rearrangements similar to acidic transitions. Isoproterenol, yohimbine diphenhydramine, chlorpromazine and atropine, which activate AdC and hinder Ca-PPI, cause conformational changes of HSA similar to basic transitions.