Physicochemical properties of arterial elastin and its associated glycoproteins

Microfibrillar glycoproteins are a significant component of vascular elasti c tissue, but little is known about their contribution to vascular physiolo gy and pathology. We have investigated so,ne physicochemical properties of the glycoproteins that may be pertinent to these roles. Because of the diff iculty in isolating intact glycoproteins in a form and quantity suitable fo r physicochemical examination, we based our analysis on a comparison of the properties of porcine thoracic aorta and pulmonary artery extracted with G uHCl and collagenase (preparation GC) and after further treatment with dith ioerythritol to remove glycoproteins (preparation GC/DTE). Amino acid analy sis showed that GC/DTE had the amino acid composition of pure elastin while GC contained a higher proportion of polar amino acids, particularly in the aortic preparation. GC stained with alcian blue, particularly in the intim al region, but GC/DTE did not. GC had a higher water content and a slower v iscoelastic response and the circumferential elastic modulus was approximat ely 50% lower (whether Expressed in terms of sample weight or elastin conte nt). Clearly, therefore, the microfibrils do not stiffen the network and ma y prevent the alignment of elastin fibers in the circumferential direction. Their effect on hydration may arise either because they impose mechanical constraints on the geometry of the network ol because they modify the inter - and intramolecular hydrophobic or electrostatic interactions that influen ce the tissue organization and hydration. Molecular probe measurements of t he intrafibrillar pore structure using radiolabeled and fluorescent probes showed that removal of the,microfibrils caused a slight decrease in the ext rafibrillar water space and a larger decrease in the intrafibrillar water s pace. Sucrose, a small probe molecule, was able to penetrate most of the in trafibrillar water space when microfibrils were present bur was virtually e xcluded when they were not. Potentiometric titration and radiotracer assays of ion binding both showed that the microfibrils contribute a considerable negative charge (-9 mu moles/g wet tissue in the aortic preparation and -1 6 mu moles/g wet weight in the pulmonary artery) and increase calcium bindi ng by approximately 30%. (C) 1999 John Wiley & Sons, Inc.