The effect of bongkrekic acid on the binding of ADP to mitochondrial membranes is characterized and studied in relation to a number of parameters.1. Bongkrekic acid increases the binding of ADP to mitochondrial membranes (from beef heart, rat heart and rat liver) in contrast to atractyloside. The "specific" ADP binding (i.e. binding at the carrier sites), under the influence of bongkrekic acid, is differentiated by the combined application of bongkrekic acid and atractyloside so that the unspecific, non-carrierlinked binding portions are substracted. The binding increase by bongkrekic acid is specific both for ADP and ATP and excludes AMP and other nucleotides such as I D P etc.2. The dependence of the binding on the concentration of ADP shows that under the influence of bongkrekic acid the affinity for ADP is increased by about 25-to 100-fold, yielding a dissociation constant KD of 0.2 to 0.02 pM. 4. The specific ADP binding is smaller when bongkrekic acid is added before than after ADP. The binding sites, differentiated by the sequence of bongkrekic acid addition, are interpreted to reflect inner binding sites which can be reached by bongkrekic acid due to its lipophilic nature. I n certain cases this difference is of equal size to the portion of high affinity sites for ADP without bongkrekic acid which previously also had been explained to represent the inner sites exposed to endogenous adenine nucleotides.5. With double labelling the binding of endogenous adenine nucleotides can be directly shown to be increased during preincubation with bongkrekic acid causing an apparent decrease in binding of exogenous ADP. Thus a t high concentration of bongkrekic acid all sites can be blocked by endogenous adenine nucleotides.6. The additional binding of ADP by bongkrekic acid is remarkably slow depending on several parameters (e.g. half-time, tlls, ranging from 0.5 to 5 min a t pH 7.0, 20 "C). Preincubation with bongkrekic acid only partially eliminates the slow time course, indicating that transition of sites to high affinity requires simultaneous presence of bongkrekic acid and ADP.7. The influence of bongkrekic acid on the binding of ADP is strongly temperature-dependent. The temperature effect is of kinetic nature since once applied at increased temperature, bongkrekic acid remains effective in the ADP binding a t lower temperature. The temperature effect is diminished a t lower p H and a t high concentration of bongkrekic acid.8. The bongkrekic acid effect on ADP binding is strongly pH-dependent. It is effective only at pH < 7.2 and completely abolished a t pH > 7.6. The pK of the bongkrekic acid effect is independent of the concentration of ADP but is increased with the concentration of bongkrekic acid. 9. Two theories are discussed : (a) a cooperative increase of the binding for ADP by bongkrekic acid, i.e., existence of substrate and regulatory sites, or (b) binding of bongkrekic acid to the substrate site of the carrier, however, preferentially when located on the inner membrane surface, resulting in a redistr...
Further unique effects of bongkrekate on the binding of ADP to the inner mitochondrial membrane are described in addition to a preceding report by us and explained so as to demonstrate the reorientation of a mobile carrier across the membrane.1. The dependence of the bongkrekate-induced increase of ADP binding is nonlinear with respect to the bongkrekate concentration. Consequently the apparent Kd for ADP decreases nonlinearly with bongkrekate concentration. The nonlinearity is kinetic in nature and is not explained by regulatory (allosteric) effects. The nonlinearity is diminished a t lower pH.2. The binding of bongkrekate appears to be dependent on ADP indicating a reciprocal enhancement effect between ADP and bongkrekate binding. As a consequence the binding of high-affinity nucleotide (such as ADP) is relatively more increased by bongkrekate than the binding of nucleotides with less affinity such as dADP. This specificity preference for ADP is also increased by bongkrekate as compared to other analogues such as formycin diphosphate, and the imidodiphosphate and methylene diphosphate derivations of adenylate. The counteraction of bongkrekate and atractylate on ADP binding also depends on the cooperation between ADP and bongkrekate.3. An apparent irreversibility of the bongkrekate-induced ADP binding is demonstrated by several effects. I n the course of time bongkrekate + ADP supersede the counteraction of atractylate, even a t higher atractylate concentration. Also carboxy-atractylate, with still higher affinity than atractylate, cannot abolish the bongkrekate.[14C]ADP once fixed with bongkrekate a t low pH cannot be removed by exchange with excess ADP or atractylate even a t pH 8, although a t this pH bongkrekate is unable to induce a binding increase. 4.The results can be explained by the "reorientation mechanism" of the bongkrekate effect by which the ADP . carrier complex is translocated inside and all carriers become trapped inside by bongkrekate as the immobile carrier . bongkrekate complex. The reciprocal enhancement of bongkrekate and ADP binding is explained by the fact, that ADP is required to move the carrier inside where bongkrekate can bind to the carrier. The irreversibility of the bongkrekate effect results from the shift of the carrier inside and the resulting removal of the carrier out of the equilibrium with external ligands such as atractylate or ADP. The results thus produce the most direct evidence so far available on the molecular level, for the existence of a mobile metabolite carrier.In a preceding report [l] principle effects of bongkrekate on the adenine nucleotide binding to mitochondrial membranes were described. Bongkrekate was found to produce a number of unique effects of which only the main features are mentioned:In view of the fact that in aqueous solution at pH 7.0 bongkrekic acid is largely dissociated to the anion, the name bongkrekate was introduced in this paper. It has the advantage of brevity as compared to bongkrekic acid. In accordance atractyloside is called atractyl...
Zusammenfassung Obwohl die erste Balintgruppe f?r Studierenden schon im 1969 stattgefunden hat ? ?Junior Gruppe Mailand? ? war die weitere Verbreitung von studentischen Balintgruppen an den Universit?ten nicht selbstverst?ndlich. Medizinstudenten haben noch in ihrem ersten Pflegepraktikum pers?nlichen Kontakt mit Patienten. Je geringer die Erfahrung und das Wissen der jungen Menschen ?ber Krankheit, Genesung und Therapie sind, desto mehr und intensiver sind die Gef?hle von Ohnmacht, Hilflosigkeit, Alleingelassensein usw. In einem Krankenhausalltag zwischen Notf?llen und Routine sind Medizinstudenten oft sich selbst ?berlassen mit der Einsch?tzung und der Frage nach einer ad?quaten Mitwirkung bzw. Reaktion in der aktuellen Situation. Im folgenden Bericht geht es um eine Gruppe mit 8 Teilnehmerinnen im 8.?10. Fachsemester Humanmedizin an der LMU M?nchen. Anhand von 4 kommentierten Fallvignetten wird die Entwicklung eines ?Lehr-Lern-Prozesses? sowohl aus der Perspektive der Gruppenleiterin als auch der Studierenden dargestellt. In der studentischen Balintgruppe standen sowohl patientenbezogene Selbsterfahrung als auch die Reflexion der sozialen Rolle des Studierenden im Krankenhaus im Zentrum. Dar?ber hinaus ging es um Verschwiegenheitspflicht, Rollenkonflikte, das Spannungsverh?ltnis zwischen Einf?hlung und professioneller Abgrenzung, insbesondere im Umgang mit sehr kranken Menschen und die Konfrontation mit Tod und Sterben.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.