FACILITATION OF PENICILLIN HAPTENATION TO SERUM-PROTEINS

Traditionally, penicillin binding to serum proteins was believed to be a passive chemical process; however, it appears to be facilitated by serum factors. The objectives of this in vitro investigation were to e xamine facilitated penicillin haptenation, to study the kinetics of ha ptenation, and to determine the nature of haptenation-facilitating fac tors. The model involved addition of [H-3]benzylpenicillin to serum or albumin solutions (at pH 7.3 to 7.4) and incubation at 37-degrees-C f or up to 72 h. The extent of penicillin binding to proteins in serum w as found to be four- to fivefold higher than with solutions having com parable concentrations of purified albumin, total protein, or total im munoglobulin. Ultrafiltration of serum reduced penicillin binding to s erum proteins substantially. An ultrafiltrable haptenation-facilitatin g factor(s) was found to be less than 0.5 kDa but was not calcium or m agnesium. Finally, the extent of penicillin binding was related to alb umin purity, as binding substantially increased with albumin purity. T hese findings suggest that there is a factor(s) in serum that facilita tes covalent binding of penicillin to serum proteins. The factor(s) ca n be removed and then restored to increase penicillin binding to album in. It appears that at least one component of the facilitation factor is less than 0.5 kDa, which suggests that it is not a peptide and that it is some simple serum component other than calcium or magnesium.