LUNG HYALURONAN AS ASSAYED WITH A BIOTINYLATED HYALURONAN-BINDING PROTEIN

This study was designed to define how hyaluronan (HA) is bound in lung tissue. Aliquots of lyophilized hamster lungs were extracted with 0.5 M NaCl (associative conditions) or 4 M guanidine . HCl (Gu . HCl) (dissociative conditions) or with water. Aliquots were also digested with Pronase in phosphate-buffered saline (PBS) or in dilute Tris buffer. The nanogram amounts of solubilized HA were quantified by an inhibition assay based on the specificity of binding of HA to biotinylated HA-binding protein (B-HABP) rather than radioactive HA-binding protein. Lung HA was readily soluble. More than 80% of it was solubilized by one extraction with either 0.5 M NaCl or 4 M guanidine . HCl. Almost half of it was solubilized by two brief (l5-min) water washes. After three extractions under associative conditions only 5% of the total HA remained insoluble and could exist in structural proteoglycan aggregates. However, HA is present in lung in more than one situation, as was discerned in Pronase digestion experiments. Digestion of lung tissue with Pronase solubilized total lung HA. in PBS all the HA was detected, but in dilute Tris buffer 52% of the HA solubilized was not available for combination with the B-HABP and was presumed to be bound to another lung component. Overall, the data suggest that lung HA is free to engage in water transport and to provide a protective coating for elastin and collagen fibers.