Dieter Seiler

Alteration of erythrocyte (Na++K+)-ATPase by replacement of cholesterol by desmosterol in the membrane

Cholesterol of red blood cells (RBC) is readily exchanged by desmosterol and vice versa. The resulting alteration in the sterol composition influences the specific (Na++K+)-ATPase activity. It is suggested that this effect is due to an altered membrane fluidity.

The ATPases of the sarcolemma from skeletal muscle in experimental myotonia

Die Aktivität der (Mg++)- und der (Na++K+)-stimulierten ATP-ase des Sarkolemm von Ratten mit Myotonie durch 20.25-Diazacholesterin ist gegenüber den Kontrollratten eindeutig erniedrigt. 2,5 mM 2,4-Dichlorophenoxyacetat im Bestimmungsansatz hemmt beide ATP-asen um ungefähr 60%.

Effect of cholesterol oxidation on (Na+, K+) ATPase activity of erythrocyte membranes.

By incubation of human erythrocyte ghosts with cholesterol oxidase (EC 1.1.3.6) part of the cholesterol of the membrane is replaced by 4-cholesten-3-one. This alteration in the sterol composition is accompanied by an inhibition of the (Na+, K+) ATPase of the erythrocyte membrane.

Transport atpases of cardiac sarcolemma in experimental uremia

Uremia was induced in rats and rabbits by unilateral nephrectomy and partial resection of the contralateral kidney. The effectiveness of the procedure was checked by determining serum urea levels that 7 days after operation were found to be more than twice as high in the operated than in the sham operated animals. Serum electrolytes at this time did not show significant alterations. In the cardiac sarcolemma from both kinds of animals the specific (Na+,K+)-ATPase activity was significantly decreased in the uremic animals. The basic, Mg2+-dependent ATPase was not affected.

Glycogen breakdown in human lymphocytes: Activities of phosphorylase and α-1,4-glucosidases

Abstract Glycogen phosphorylase (E.C. 2.4.1.1) and acid and neutral α-1,4-glucosidase (E.C. 3.2.1.20) have been demonstrated in pure homogenates of circulating lymphocytes from normal persons by biochemical analyses. Quantitation of the enzymes has been established in terms of their catalytic activity and levels of lymphocyte enzymes compared with those of leucocytes (mixture of granulocytes and lymphocytes) found by other investigators and ourselves. Preparation of lymphocytes for biochemical analyses requires certain modifications of the usual technical and special precautions which have been described in detail. The influence of exogenous glucose has also been investigated.

Transport-ATPasen bei experimenteller Myopathie

Durch 20,25-Diazacholesterin konnen beim Menschen und beim Tier die Symptome einer Myotonie hervorgerufen werden. Die Substanz hemmt die Cholesterinbiosynthese auf der Stufe der Umwandlung des Desmosterin zum Chole sterin. Desmosterin, das sich vom Cholesterin lediglich durch eine zusatzliche Doppelbindung in der Seitenkette unterscheidet und bei unbehandelten Tieren nur in sehr kleinen Mengen zu finden ist, wird unter 20,25-Diazacholesterin-Behandlung angereichert. Im Serum und allen Organen des Tieres scheint es weitgehend das Cholesterin zu ersetzen, denn die Gesamtsterinmenge bleibt auch nach monatelanger Verfutterung von 20,25-Diazacholesterin praktisch konstant. Dieser Ersatz des Cholesterins durch seine Vorstufe geht jedoch in verschiedenen Organen verschieden schnell vor sich, und auch verschiedene Zellfraktionen eines Organes zeigen diesbezuglich ein unterschiedliches Verhalten. Unterschiedlicher Sterin-gehalt, schnellerer oder langsamerer Turnover oder eine unterschiedliche Affinitat der Membranen fur die beiden obengenannten Sterine mogen hierfur eine Rolle spielen [1].