Gamma-glutamyl transpeptidase in brain capillaries: possible site of a blood-brain barrier for amino acids

A fraction containing capillaries and rich in gamma-glutamyl transpeptidase was isolated from homogenates of bovine brain cortex by density gradient centrifugation. The enzyme was localized in the endothelial cells by a histochemical procedure. gamma-Glutantyl transpeptidase may function in the transfer of some amino acids across the blood-brain barrier.

Localization of transport adenosine triphosphatase in rat cornea

Increasingly, physiological and biochemical data on the mammalian cornea have emphasized the importance of the endothelial rather than the epithelial layer in regulating the state of hydration of the cornea, via a transport ATPase. This view is supported by the observations reported here. With the Ernst method, the first cytochemical procedure to be readily responsive to ions and ouabain, the major sites of enzyme reaction product are the intercellular spaces of the endothelial layer. This localization was not found by us with the so-called ATPase method of Wachstein and Meisel.

Microchemical determination of enzyme activities in the lathyritic chick embryo aorta

In a study of lathyrism in the chick embryo, β-aminopropionitrile (β-APN) was found to alter the appearance of elastic material in the aortic media. Histochemical observations showed that, both in normal and in lathyritic aortas, alkaline phosphatase (APase) activity was localized to the endothelium. Glucose-6-phosphate dehydrogenase (G-6-PDH), malate dehydrogenase (MDH), lactate dehydrogenase (LDH) and acid phosphatase (AcPase) activities were demonstrable mainly in the endothelium and in the media. The activities of these 5 enzymes were measured microchemically in freezedried aortic sections. Simultaneous determinations were made in normal 17-day embryos and in 17-day embryos that had been treated with β-APN 3 days previously. In addition, G-6-PDH activity was measured in 15-day normal and 15-day lathyritic chick embryo aortas 24 hours after beginning treatment with the nitrile.

The activities of the oxidative enzymes and AcPase expressed on a dry weight basis increased significantly in the aortas of the lathyritic animals. However, APase activity remained unchanged. It is suggested that β-APN influences the metabolic activity of aortic medial muscle cells in addition to inhibiting the cross-linking of extracellular elastin. This observation conforms with the electron microscopic evidence that the medial cells of lathyritic aortas display structural abnormalities. The possibility that the loss of preformed elastic material from the vessel wall in lathyrism may be the result of changed lysosomal permeability is discussed.

[Enzyme histocytochemical studies of atrioventricular heart valves in endocardiosis in the dog]

Enzyme histochemical studies were performed on normal atrioventricular heart valves and valves with different stages of endocardiosis in the dog. The enzymes studied wereß-glucuronidase, N-acetyl-ß-glucoseaminidase, AMPase, ATPase and glucose-ß-phosphate dehydrogenase. Increased enzymatic activity was seen in cases of endocardiosis in auricular endothelial cells, in subendothelial so-called reactive cells (smooth muscle cells, macrophages, fibroblasts) and in fibroblasts of proliferation areas of the valve. The significance of an increased catabolic and anabolic metabolism in the pathogenesis of canine endocardiosis and the possible relationship to arteriosclerosis are discussed.