Moving Questions: A History of Membrane Transport and by Joseph D. Robinson

By Joseph D. Robinson

This booklet describes part a century of development in mainstream parts of organic learn: membrane shipping, first and foremost a spotlight of physiologists, and oxidative phosphorylation, before everything a spotlight of biochemists. Robinson indicates how the improvement of recent explanatory versions had all of sudden merged those inquiries right into a new box, bioenergetics. within the overdue Nineteen Thirties, causes for the uneven distribution of ions among cells and their environments invoked absolute impermeabilities of the cell's surrounding membranes. yet new experiments contradicted that concept and validated that forming the transmembrane distributions required metabolic power, implying the participation of lively delivery "pumps." next stories pointed out, remoted, and characterised those pumps as enzymes coupling ionic shipping to the intake of adenosine triphosphate (ATP), an "energy-rich" molecule serving as a mobile power shop. within the overdue Nineteen Thirties oxidative phosphylation, the method of coupling ATP synthesis to oxidative metabolism, was once pointed out. The explanatory version rising within the subsequent a long time, despite the fact that, didn't keep on with the enzymatic precedents of recognized metabolic phosphorylations yet particularly embodied the primary that metabolic oxidations force lively delivery pumps to create transmembrane distribution of ions, with those ionic asymmetries then riding ATP synthesis. It used to be found that ATP intake can shape ionic asymmetries; ionic asymmetries can force ATP formation; and ionic asymmetries-like ATP-can additionally strength different mobile features.

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Extra resources for Moving Questions: A History of Membrane Transport and Bioenergetics

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Conway's Formulation Conway saw in muscle the realization of mechanism 3. This formulation he published with P. J. Boyle 12 in a severely abridged form in 1939 and in a lengthy exposition in 1941; the latter will be considered here. MOVING QUESTIONS 32 Membranes, according to this model, were permeable to K+ and H+, although they were impermeable to larger cations like Na +. But they were permeable also to smaller anions like cl-. This permeability to cl- represented a major break with previous assumptions, but it was founded on direct evaluation by Conway as well as on descriptions for some tissues of cl- volumes that were larger than Na + volumes.

Conway also attacked Krogh's claim that Na+ influx was at least as great asK+ influx, thus applying option 2. 5 mM K+ to media containing 10 mM K+. 62 To evaluate Krogh's claim, he set Na+ influx equal to this calculated K+ influx. Conway next calculated the rate of Na+ outflux from muscle and its energy cost (the switch here from influx to outflux was justified by the two fluxes having to be equal, or a net gain or loss of Na+ would result). Conway then reported that such aNa+ outflux would cost 350 cal per kilogram of muscle/hour; that value he converted to oxygen consumption,63 which he then stated was "about twice as much, or more, [than the] resting muscle metabolism of ...

Fenn. ) intuitively appealing and reflected the ability of porous artificial membranes then being studied to discriminate similarly. 2. Membranes were impermeable to anions (imaginable as negatively-charged pores accepting positively-charged ions but rejecting negatively-charged ones). This postulate thus barred cl- , the major extracellular anion, from entering or leaving cells; Fenn referred to "the general agreement that .. muscle is normally impermeable to chloride. 7% of the total muscle fluid volume, which was close to the extracellular volume estimated from microscopic examination of muscle.

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