Regulatory Mechanisms of the Calcium Transport System of Fragmented Rabbit Sarcoplasmic Reticulum : II. Inhibition of outflux in calcium-free media

The outflux of calcium from vesicles of sarcoplasmic reticulum is controlled by the concentration of ionized calcium in the medium. In a calcium-free medium calcium outflux is at a minimum provided ATP and Mg are present. If they are removed calcium outflux becomes rapid and has a rate constant similar to that of outflux during steady-state ⁴⁰Ca-⁴⁵Ca exchange with saturating calcium concentrations in the medium. In order to maintain the low permeability state of the membrane only the presence but not the continued hydrolysis of ATP is necessary.     

Stomata-Anomalie vonOpuntia-Virusträgern

Zusammenfassung Die Spaltöffnungsapparate von Kakteen (Opuntia. Epiphyllum, Rhipsalis), die in den Epidermiszellen Eiweißspindeln enthalten, degenerieren häufig oder weisen eine abnorme Entwicklung auf. So kommen bei den Blättern vonOpuntia subulata zahlreiche Zwillingsspaltöffnungen vor, die aus einer Mutterzelle hervorgehen (eineiige Zwillinge). Die Eiweißspindeln werden als Virus-Körper aufgefaßt und es wird vermutet, daß die gehäufte Bildung der abnormen Stomata mit der Virusinfektion zusammenhängt, obwohl die Schließzellen der Kakteen keine Virus-Einschlußkörper enthalten. Die Abnormitäten und Verkümmerungen des Spaltöffnungsapparates wären demnach ein mikroskopisch sichtbares Symptom an äußerlich symptomlosen Virusträgern.     

Oligomeric protein associations: transition from stochastic to deterministic equilibrium

Transfer of electronic excitation energy (sensitized fluorescence) between donor and acceptor fluorophores separately attached to dimer or tetramer proteins is used to demonstrate the exchange of subunits among the undissociated particles. In dimers subjected to a pressure that produces half-dissociation, the exchange occurs at a rate that approaches the rate of dissociation. In the tetramers of glyceraldehydephosphate dehydrogenase and lactate dehydrogenase at 0 degrees C, the times for subunit exchange are nearly 2 orders of magnitude, and at room temperature 5-10 times longer than the time required to reach the dissociation equilibrium. By application of a novel method, pressure is shown to preferentially increase the rate of dissociation in dimers and decrease the rate of association in tetramers. From these observations, we conclude that the tetramers constitute a heterogeneous population, the members of which are dissociated by pressure according to individual molecular properties that can be retained over periods of time much longer than the time for equilibration of the dissociation. The dissociation of dimers exhibits the characteristics of the classical stochastic chemical equilibria, while those of the tetramers, like the more complex protein aggregates, must already be considered similar to the deterministic mechanical equilibria of macroscopic bodies.     

Metabolism of ether glycolipids with potentially antineoplastic activity by Ehrlich ascites tumor cells

Ehrlich ascites tumor cells were incubated in vitro with rac-1-O-[1'-14C]octadecyl-2-O-methylglycero-3-beta-D-glucopyranosi de for 24 h. The potentially antineoplastic ether glycolipid was rapidly metabolized by the cells to radioactive 1-O-octadecyl-2-O-methylglycerol (70 pmol/10(6) cells per h) and further acylated to 1-O-octadecyl-2-O-methyl-3-acylglycerols. Incubation of Ehrlich ascites cells with synthetic rac-1-O-[1'-14C]octadecyl-2-O-methyl-3-palmitoylglycerol showed that this metabolite is reconverted by deacylation to 14C-labeled 1-O-octadecyl-2-O-methylglycerol. The latter compound or a metabolite derived therefrom may be the 'toxic principle' of both the ether glyceroglycolipids and ether glycerophospholipids having a 1-O-alkyl-2-O-methylglyceryl moiety, as suggested by Unger et al. (J. Natl. Cancer Inst. 78 (1987) 219-222).