. Biological structure and function; proceedings. Biochemistry; Cytology. COMPONENTS OF THE ENERGY-COUPLING MECHANISM 43 contract quite well in a butfered KCl medium on addition of ATP. The addition of ATP + Mg ^ + + serum albumin was found to cause immediate contraction of mitochondria swollen by a wide variety of agents, including thyroxine, oleate, phlorizin, calcium, PCAIB, phosphate, and many others [44] and, curiously, mitochondria swollen by digitonin and by carbon tetrachloride. Actual extrusion of water was demonstrated by gravimetric methods to accompany the optical changes. It was s
. Biological structure and function; proceedings. Biochemistry; Cytology. COMPONENTS OF THE ENERGY-COUPLING MECHANISM 43 contract quite well in a butfered KCl medium on addition of ATP. The addition of ATP + Mg ^ + + serum albumin was found to cause immediate contraction of mitochondria swollen by a wide variety of agents, including thyroxine, oleate, phlorizin, calcium, PCAIB, phosphate, and many others [44] and, curiously, mitochondria swollen by digitonin and by carbon tetrachloride. Actual extrusion of water was demonstrated by gravimetric methods to accompany the optical changes. It was shown that several hundred moles of water could be extruded per mole of ATP split [34]. The molecular mechanism of the ATP-induced contraction can be shown to be completely independent of respiration and net phosphoryla- tion, since it proceeds perfectly well in a medium containing sufficient. P:0 = 2- K^ = i2m/^M/MG P:O = 00 K^=OOI Q 03 [PO^OO iK* =002 Time (rnin) Fig. 5. Independence of ATP-induced contraction from oxidative phosphoryla- tion and K ~ binding. .Allowing mitochondria to stand in swollen state at 25 for extended periods abolishes phosphorylation and K ^-binding, without affecting abilitv to contract. cyanide or other respiratory inhibitors to block respiration or in the presence of sufficient dinitrophenol to completely uncouple oxidative phosphorylation, as long as ATP is in excess [34]. On the other hand, it is clear that the ATP-induced contraction must employ at least a portion of the energy coupling machinery, since this contraction is blocked by inhibitors such as azide, which disconnects the ATP-ADP exchange reaction from the dinitrophenol sensitive site, and is also inhibited characteristically by sucrose and many other sugars and polvhvdroxvlic alcohols, which are also known to inhibit oxidative phosphorylation and the ATP-P^'- exchange reaction as well as ATP-ase [3^]. Furthermore, contraction of mitochondria by ATP is not dependent on any specific ioni
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