Search

The activity of phosphofructokinase-2, fructose, 1,6-bisphosphatase, glucokinase, and also the level of fructose 2,6-bisphosphate and glycogen were examined in the liver of normal, and streptozotocin-diabetic rats. It was shown that the activity of phosphofructokinase-2 was decreased in the liver of diabetic rats. Besides that the activity determined at pH 6.6 (the "active" or unphosphorylated enzyme form) was 3-fold reduced whereas the "total" enzyme activity as measured at pH 8.5 was lowered 1,7-fold. The phosphofructokinase-2 activity assay at two pH values allows to estimate a degree of phosphorylation of bifunctional enzyme which is markedly enhanced in diabetes. The fall of the bifunctional enzyme k in case activity is accompanied by the lowered fructose 2.6-bisphosphate level, increased fructose 1,6-bisphosphatase activity that in turn favours the liver tissue glycolysis inhibition and gluconeogenesis enhanced in diabetes.

The molecular mechanisms of the inhibitory action of fructose- 2,6-bisphosphate (F-2,6-P2) on fructose-1,6-biphosphatase (FB-Pase-1), the key enzyme of gluconeogenesis, and the those of the activating action of F-2,6-P2 on phosphofructo-1-kinase (PFK-1), the key enzyme of glycolysis, NMR spectroscopy first provided direct evidence for the fact that F-2,6-P2 was involved in the regulation of the sedoheptulose cycle of a nonoxidative stage of the pentosephosphate pathway. Procedures were developed in measuring the levels of F-2,6-P2 in the cell of experimental animal tissues and human blood lymphocytes. Naturally different emergencies substantially affected the F-2,6-P2 system by triggering these or those mechanisms controlling the activity of enzymes of this system. Vanadium-containing compounds were demonstrated to have a positive action on carbohydrate metabolism in diabetic (streptozotocin-induced) rat hepatocytes.

Hyperbaric oxygenation (HBO) effects on the levels of circulating glycosylated proteins with various life spans in the blood stream (glycosylated hemoglobin (GH) and serum glycosylated fructose amine (SF) were studied in diabetes mellitus patients not suffering from vascular complications but developing various microangiopathies. Measurements of blood glycosylated proteins and mean daily glycemia carried out over the course of HBO treatment in the diabetics without microangiopathies evidenced an essential reduction of blood GH, SF, and glucose, reaching, in some cases, the normal values. Patients with vascular involvement (lower limb angiopathy, nephropathy, retinopathy) exposed to HBO developed but a trend to reduction of blood levels of glycosylated proteins and glucose. These results indicate a positive therapeutic effect of HBO courses on the status of diabetics with slightly manifest microvascular involvement. In cases with grave vascular involvement exposure to HBO appears inefficient.

A method for measuring non-enzymatically glycosylated albumin and hemoglobin in a single blood sample is described. It is advisable that these proteins be assayed separately, because albumin metabolism rate is higher than that of hemoglobin and therefore glycosylated hemoglobin may be regarded as a criterion for diagnosing diabetes mellitus and the level of glycosylated albumin as an indicator of diabetes mellitus compensation and a characteristic that permits monitoring the course of treatment. The method consists in preparation of the blood erythrocytic mass and plasma, followed by trichloracetic acid hydrolysis of glycosylated hemoglobin and glycosylated albumin during heating and assay of the resultant fructose forming a colored complex with thiobarbituric acid. Twenty-nine normal subjects were examined with the use of this method; the mean arithmetic (means +/- m) has made up 3.68 +/- 0.21 mumols of fructose glycine per g of hemoglobin for glycosylated hemoglobin and 27.0 +/- 1.78 mumols of fructose glycine per g of albumin for glycosylated albumin. In diabetics these values were several times higher and the mean arithmetic value of glycosylated hemoglobin was 20.5 +/- 0.45 mumols of fructose glycine per g of hemoglobin and that of glycosylated albumin 63.8 +/- 1.7 mumols of fructose glycine per g of albumin (n = 42), the significance of differences being p less than 0.001.

125I-labelled human serum low density lipoproteins (LDL) were incubated with cultured mouse peritoneal macrophages at 37 degrees C, with the following study of cellular uptake and 125I-LDL degradation by measuring the content of TCA-soluble products of LDL hydrolysis in the cultural medium. It was shown that limited pepsin proteolysis of LDL (10%) led to a more effective LDL uptake and degradation by macrophages. The data suggest that enzyme-induced modification of LDL may increase their atherogenicity.