Production of Human Type Glycosylated Tissue Plasminogen Activator and the Role of Its Carbohydrate Moiety

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To begin the examination of the role of human type carbohydrate moiety of tissue plasminogen activator (t-PA) on the binding of the enzyme to fibrin，the naturally glycosylated enzyme was produced by microcarrier culture of human cells established from normal uterine muscle. The cells grown on microcarrers in Haunks' MEM supplemented with 10 % FBS (1.6 x 10 6 cells/ml) rapidly detached themselves from microcarrier in a serum-free medium (t-PA production medium) within 5 days, and it was difficult to produce t-PA for long time (t-PA production: an average of 3 IU/ml/day over 5 days). Addition of 0.5% beef extract to the serum-free medium suppressed their detaching from microcarriers. By regulating the pH (7.4) and dissolved oxygen(4 ppm) of the serum free medium，the cell density of microcarrier culture increased to 1.2 x10 7 cells/ml and t-PA was produced over 38 days (t-PA production: an average of 836 IU/ml/day over 38 days). Native t-PAs purified to homogeneity from the culture broth had the molecular weight of 63,000 and 65,000 containing 5.6 and 8.5 % carbohydrate，respectively (molecular mass of protein moiety was calculated to be 59,500). By enzymatic digestion of carbohydrate moiety in native t-PA，we obtained partially deglycosylated t-PA with molecular weights of 60,000 and 62,000. Completely deglycosylated t-PA was obtained by t-PA production in the presence of 10μg/ml tunicamycin (N-glycosylation inhibitor). This suggests that N-glycosylationof t-PA occurs while O-glycosylation is absent. The binding strength of these enzymes to fibrin increased with decrease of the carbohydrate content. The carbohydrate moiety of human type glycosylated t-PA probably modulates the binding strength of the enzyme to fibrin.

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