Open AccessKinetic Mechanism of the Exchanges Catalysed by the Adenine‐Nucleotide Carrier
Author(s) -
DUYCKAERTS Claire,
SLUSEGOFFART Claudine M.,
FUX JeanPierre,
SLUSE Francis E.,
LIEBECQ Claude
Publication year - 1980
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1980.tb05990.x
Subject(s) - ternary complex , ternary operation , nucleotide , chemistry , cooperativity , mechanism (biology) , intersection (aeronautics) , kinetic energy , stereochemistry , biophysics , thermodynamics , physics , biochemistry , enzyme , biology , computer science , quantum mechanics , aerospace engineering , engineering , gene , programming language
Initial rates of the exchange ADP in /ADP out catalysed by the adenine‐nucleotide carrier of rat‐heart mitochondria have been studied under conditions where internal and external ADP may be varied. The initial rate was measured within 1 s by the carboxyatractyloside‐stop method, using a rapid‐mixing technique. The double‐reciprocal plots V 0 −1 versus [ADP] out −1 at different internal‐ADP concentrations and V 0 −1 versus [ADP] in −1 at different external‐ADP concentrations exhibit straight‐line relationships having a common point of intersection on the axis of ordinates. These results demonstrate the essential role of a ternary complex and thus exclude the ping‐pong mechanism generally accepted. The kinetic equation implies a strong positive cooperativity in the binding of the two substrates. Two models are proposed: (a) the ternary complex performs the exchange and the transport of the substrates in a single step; (b) the carrier is mobile and transports the substrates one by one, the formation of a ternary complex being needed to release the first product.