Summary.Fibrinogen was purified from plasma from 22 nondiabetic and 26 poorly controlled Type I (insulin-dependent) diabetic subjects. In non-diabetic subjects, 0.95+0.17mol glucose was bound per mol fibrinogen, whereas in the diabetic subjects 1.33 + 0.21 mol glucose was bound per tool fibrinogen (mean + SD, p < 0.001). Comparison of the amount of bound glucose, when estimated by two different methods, suggested that lysine is the site of glycosylation. It is currently unknown whether this increased glycosylation of fibrinogen alters its function.Key words: Fibrinogen, glycosylation, Type I diabetes.Glucose has been shown to bind non-enzymatically and irreversibly to all types of protein through Schiff-base formation and Amadori re-arrangement to a ketoamine [1]. This glycosylation appears to be dependent on the duration of exposure and glucose concentration in the surrounding medium. Glycosylation occurs either on the amino terminal end of the protein, as with haemoglobin [2], or on the free amino group of lysine. Because of this glycosylation, the tertiairy or quaternary structure, function and/or degradation of the protein molecule may be altered, as has been demonstrated with glycosylated haemoglobin (HbA0 Fibrinogen is a protein with a half-life of 3-4 days, which occupies a central position in blood clotting. It is known that the e-amino groups of lysine in the fibrinogen molecule play an important role in cross-linking fibrin monomers and in fibrinolysis. We have therefore investigated whether glycosylation of fibrinogen is increased in the blood of diabetic patients. Subjects and methods SubjectsTwenty-two healthy volunteers (aged 21-59 years, mean 33 years; mean blood glucose level at the time of sampling, 5.1 _+ 1.0 mmol/1) and 26 Type 1 (insulin-dependent) diabetic patients (aged 19-57 years, mean 36 years; taking no medication other than insulin) participated in the study. MethodsBlood was collected in 3.2% sodium citrate (1 : 10, wt/vol) for purification of fibrinogen and estimation of glycosylation. After centrifugation at 5000 g for 20 min, plasma was either processed immediately or stored at -26~ Blood was also taken for estimation of glucose and HbAv HbA1 was estimated by the microcolumn method ([solab In-

Summary. Polymerisation and crosslinking of fibrin monomers was studied in 35 healthy volunteers and in 42 poorly controlled diabetic patients. Polymerisation did not show any difference between control subjects (n = 10) and diabetic patients (n = 11) (p > 0.1), although fibrinogen was 35% more glycated in the diabetic patients (/)<0.001). Alpha chain crosslinking in the diabetic patients, however, was impaired as is shown from an increase in intermediate alpha polymers with a concomitant decrease in alpha monomer disappearance. A significant positive correlation was found between the degree of glycation of fibrinogen and the defective alpha chain polymerisation (r = 0.86, p < 0.005). These results were consistent with the results of thrombin and reptilase experiments. The reaction rate with reptilase did not show any difference between the two groups (p > 0.1), whereas the reaction rate with thrombin was significantly slower in the diabetic group compared to the control subjects (p < 0.001). Purified fibrin clots obtained from the diabetic patients were more susceptible to plasmin than clots obtained from control subjects. It is concluded that in poorly controlled diabetic patients polymerisation of fibrin monomers is normal, but crosslinking of the alpha chains is impaired, leading to a higher susceptibility of the clots to plasmin degradation.