Glucose 6-phosphate and hexokinase can be used as an ATP-regenerating system by the Ca(2+)-ATPase of sarcoplasmic reticulum.
In the presence of hexokinase, vesicles derived from the sarcoplasmic reticulum of skeletal muscle are able to accumulate Ca2+ in a medium containing ADP and glucose 6-phosphate. No significant Ca2+ uptake is observed if one of these components is omitted from the assay medium. Due to its high affinity for ATP, the Ca(2+)-ATPase can use the very low concentrations of ATP formed from glucose 6-phosphate and ADP to form a Ca2+ gradient. This finding indicates that glucose 6-phosphate and hexokinase can be used as an ATP-regenerating system. The Ca2+ uptake supported by glucose 6-phosphate and ADP is inhibited by glucose and D-xylose. Half-maximal inhibition is observed in the presence of 0.4 mM glucose and 100 mM D-xylose. The transport ratio (Ca2+ transported:substrate utilized) is the same for glucose 6-phosphate and ATP. The Ca2+ gradient formed when glucose 6-phosphate and ADP are the substrates can be used to synthesize ATP from ADP and Pi. The concentration of ATP formed after reversal of the Ca2+ pump is much higher than that expected from direct equilibration of the reaction between glucose 6-phosphate and ADP.
Montero-Lomelí
M
M
Departamento de Bioquimica, Universidade Federal do Rio de Janeiro, Cidade Universitaria, Brazil.
de Meis
L
L
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D000252:Calcium-Transporting ATPases / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology*; D005947:Glucose / Q000494:pharmacology; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism*; D007700:Kinetics; D009132:Muscles / Q000201:enzymology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D014994:Xylose / Q000494:pharmacology
D005958:Glucosephosphates; D019298:Glucose-6-Phosphate; D000255:Adenosine Triphosphate; D014994:Xylose; D006593:Hexokinase; D000252:Calcium-Transporting ATPases; D005947:Glucose