Dacron-reinforced fibrocollagenous tubes (FCT) were synthesized from canine mongrels using the mandril-rod technique in order to develop a small diameter (i.e., 4 mm i.d.) vascular graft. They were rendered fibrinolytic by immobilizing urokinase on to the inner surface of the tubes. Urokinase-bound fibrocollagenous tubes (UK-FCT), control FCTs (i.e., no bound enzyme), Perloff grafts (Dr. Perloff, Department of Surgery, University Medical Center, Sidney Australia, has developed a mandril-derived collagenous tube from goats. Samples were implanted for comparative purposes.) and autogeneous saphenous veins, were interposed in the carotid or femoral artery in chronic studies involving 21 canine mongrels. On the basis of Doppler auscultation and palpation, the UK-FCTs were statistically more patent than other candidate prostheses. Fibrin degradation product (FDP) increased in the dogs' systemic circulation with a postoperative peak of 5 days. The host's increase in fibrinolytic activity was shown to be local to the anastamosis. A carotid arterial extracorporeal shunt was designed to evaluate acute patency. Results indicated a rapid thrombosis but no platlet or fibrin adherence to the graft surface was observed, as evidenced by scanning electron microscopy.

SummaryThe effect of a nonionic surfactant, polyoxyethylenesorbitan monolaurate (Tween 20), on the hen egg-white lysozyme catalyzed lysis of a dried cell suspension of Micrococcus lysodeikticus is analyzed. A rate enhancement of up to 70% is observed in the presence of surfactant a t concentrations above the critical micelle concentration. This activity increase may be explained by postulating the existence of a micelle-enzyme complex in which enzyme molecules are bound to micelles with preferential orientation of their active sites.A mechanism is postulated in which a substrate particle is assumed to be an energy-furnishing collision partner to the enzyme-substrate complex. This mechanism correlates data over a wide range of enzyme and substrate concentrations.Data from kinetic, ultrafiltration, ultraviolet, and fluorescence studies provide convincing evidence for the existence of a micelle-lysozyrne complex. The results suggest that it is possible that immobilized enzymes may in general be more reactive than corresponding free enzymes.The reaction is found to be second order with respect to substrate.

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In this study, L-Asparaginase has been bound to collagen heterografts derived from carotid bovine arteries. The immobilization procedure utilizes both non-covalent and covalent interactions to fix the enzyme. Binding of the enzyme to the graft material was shown to the pH dependent, with optimum binding occurring at pH 6.0 and pH 8.5. Amidohydrolysis by the bound enzyme exhibited zero-order kinetic behavior at substrate saturating conditions. Total apparent asparaginase activity expressed by the grafts as a function of the number of repeated in vitro assay trials demonstrated that over a span of 3 months of intermittent storage and use, the enzyme-grafts retained as much as 62% of their initial activities. Implantation of 4 asparaginase-collagen grafts in various locations of the thoracic and abdominal aorta resulting in prolonged reductions of plasma asparagine levels in 3 of the 4 implants. Presence of plasma asparaginase was checked in one of the four implants and determined to be less than 2 X 10(-4) I.U./ml. Removal of grafts from 3 of the 4 animal subjects showed reductions in the apparent asparaginase activity expressed by the grafts of 7 to 70 percent after in vivo contact times which varied from 6 to 15 days.

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