Abstract
Plasminogen isolated from 60 full-term newborns differs from adult plasminogen in carbohydrate composition, kinetic activation constants, and cell binding. Amino acid composition and amino-terminal sequence analysis data indicate that the plasminogens of neonates and adults have the same amino acid sequence. Like the adult, the neonate has two glycoforms, but both have significantly more mannose and sialic acid than the adult forms. The difference in the neonatal glycosylation is probably responsible for the altered migration observed by isoelectric focusing. Moreover, the difference in carbohydrate composition appears to be the basis of the decreased functional activity of the neonatal plasminogen. The kcat/Km ratios indicate that the overall activation rates of the two neonatal plasminogen glycoforms are lower compared with the adult glycoforms. In addition, neonatal plasminogen does not bind as well to cellular receptors compared with adult plasminogen. These studies suggest a basis for the decreased fibrinolytic activity observed in neonates.