Synthesis of ATP by the simple addition of ADP to the p-nitrophenyl phosphate-prepared phosphoenzyme of the sarcoplasmic reticulum Ca2+-ATPase.
The sarcoplasmic reticulum Ca2+-ATPase was phosphorylated with either p-nitrophenyl phosphate (pNPP) or with ATP in the presence of Ca2+, under the condition that the free energy change of pNPP hydrolysis is less than that of ATP, DeltaG'(pNPP)<DeltaG'(ATP), or the condition that DeltaG'(pNPP) approximately DeltaG'(ATP), without any additional energy input. In both cases, the pNPP-prepared phosphoenzyme synthesized ATP upon the simple addition of ADP, as did the phosphoenzyme prepared with ATP. The sensitivity of these phosphoenzymes to ADP for the synthesis of ATP was the same. In other words, there is no hysteresis of the phosphate donor to its DeltaG' value in these phosphoenzymes. This result means that both phosphoenzymes by themselves must have sufficient conformational energy, independent of the DeltaG' value of the phosphate donor, for the reversed synthesis of ATP, because a high-energy phosphate donor (ATP) cannot be formed from a lower-energy phosphate donor (pNPP).
Ushimaru
Makoto
M
Department of Chemistry, Kyorin University School of Medicine, Mitaka, Tokyo 181-8611, Japan. ushimaru@kyorin-u.ac.jp
Fukushima
Yoshihiro
Y
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D000818:Animals; D009596:Nitrophenols / Q000737:chemistry; D009943:Organophosphorus Compounds / Q000737:chemistry; D010750:Phosphoproteins / Q000378:metabolism*; D011817:Rabbits; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*; D013816:Thermodynamics
D009596:Nitrophenols; D009943:Organophosphorus Compounds; D010750:Phosphoproteins; C008644:nitrophenylphosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases