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The Na,K-ATPase is essential to all animals, since it maintains the electrochemical gradients that energize the plasma membrane. Naturally occurring inhibitors of the pump from plants have been used pharmaceutically in cardiac treatment for centuries. The inhibitors block the pump by binding on its extracellular side and thereby locking it. To explore the possibilities for designing an alternative way of targeting the pump function, we have examined the structural requirements for binding to a pocket that accommodates the two C-terminal residues, YY, in the crystal structures of the pump. To cover the sample space of two residues, we first performed docking studies with the 400 possible dipeptides. For validation of the in silico predictions, pumps with 13 dipeptide sequences replacing the C-terminal YY were expressed in Xenopus laevis oocytes and examined with electrophysiology. Our data show a significant correlation between the docking scores from two different methods and the experimentally determined sodium affinities, which strengthens the previous hypothesis that sodium binding is coupled to docking of the C-terminus. From the dipeptides that dock the best and better than wild-type YY, it may therefore be possible to develop specific drugs targeting a previously unexplored binding pocket in the sodium pump., QC 20220126

Fosfor (P), som udskilles med gødning fra grise og som spredes ud på de dyrkede marker, kan forårsage problemer i vandmiljøet. I Danmark (DK) har politiske krav øget opmærksomheden på reducering af denne P udskillelse, og et af værktøjerne til denne reducering er at øge (tilsyneladende) P fordøjelighed af foder fodret til grise. Størstedelen af P i frø og korn er bundet til fytat (fytat-P). Enzymet fytase er nødvendigt for hydrolyse af fytat-P for at gøre det tilgængeligt for absorption i grisen. Grisen selv danner ikke nok fytase, derfor kan mikrobiel fytase tilsættes foderet og derved øge P fordøjeligheden. Frø og korn brugt som foderingrediens indeholder naturlig fytase, som også kan øge P fordøjeligheden. Nogle kornsorter (f.eks. hvede og byg) indeholder mere naturlig fytase end andre (f.eks. majs), og der kan være en vekselvirkning mellem naturlig fytase fra en kornsort og fytat-P fra en anden kornsort indeholdt i samme foderblanding. Når foderblandinger formuleres og optimeres antages imidlertid additivitet af fordøjeligt P. Majs er ved at blive en mere almindelig anvendt foderingrediens i foderblandinger til grise i DK sammen med hvede og byg, som har været brugt i mange år. Viden omkring P fordøjelighed i majs bygger på udenlandske studier, og ingen studier har undersøgt P fordøjelighed af majs, hvis det fodres som den eneste foderingrediens til grise. Yderligere bliver tilsætning af mikrobiel fytase mere anvendt, og mikrobiel fytase har vist sig at være mere effektiv i foderingredienser med lav aktivitet af naturlig fytase end i foderingredienser med høj naturlig fytase aktivitet. På denne baggrund blev P fordøjeligheden af majs fodret som den eneste foderingrediens til slagtesvin undersøgt, og hypotesen, at fordøjeligt P er ikke-additivt i hvede, byg og majs, blev testet. Endelig blev effekten af mikrobiel fytase tilsat en blanding af hvede, byg og majs bestemt. Det blev gjort ved at udføre et balance- og fordøjelsesforsøg med 24 slagtesvin, som blev fodre, Phosphorus (P) excreted via manure from pigs and applied to cultivated fields may cause problems in the aquatic environment. In Denmark (DK), political demands have increased the attention to decrease this P excretion and one of the tools to do so is increasing (apparent) P digestibility of feed fed to pigs. The major part of P in seeds and cereals is bound to phytate (phytate-P). The enzyme phytase is needed for hydrolysis of Phytate-P, to make it available for absorption in the pig. The pig does not generate enough phytase itself, therefore microbial phytase can be added to the feed and thereby increase the P digestibility. Seeds and cereals used as feed ingredients contain intrinsic phytase, which also can increase the P digestibility. Some cereals (e.g. wheat and barley) contain more intrinsic phytase than others (e.g. maize), and there may be an interaction between intrinsic phytase from one cereal and phytate-P from another cereal contained in the same diet. However, when compound diets are formulated and optimized, additivity of digestible P is assumed. Maize is becoming a more commonly used feed ingredient in compound diets for pigs in DK, together with wheat and barley, which have been used for several years. The knowledge about P digestibility of maize builds on foreign studies, and no study has investigated the P digestibility of maize when fed as the only feed ingredient to pigs. Furthermore, microbial phytase added to pig diets is becoming more applied, and microbial phytase have been shown to be more efficient in feed ingredients with low activity of intrinsic phytase than in feed ingredients with high intrinsic phytase activity. On this background, the P digestibility of maize when fed as the sole feed ingredient to growing-finishing pigs was studied, and the hypothesis, that digestible P is non-additive in wheat, barley and maize, was tested. Finally, the effect of adding microbial phytase to a mixed diet of wheat, barley and maize was determined. It