Relationship of tightly bound ADP and ATP to control and catalysis by chloroplast ATP synthase
Whether the tightly bound ADP that can cause a pronounced inhibition of ATP hydrolysis by the chloroplast ATP synthase and F/sub 1/ ATPase (CF/sub 1/) is bound at catalytic sites or at noncatalytic regulatory sites or both has been uncertain. The authors have used photolabeling by 2-azido-ATP and 2-azido-ADP to ascertain the location, with Mg/sup 2 +/ activation, of tightly bound ADP (a) that inhibits the hydrolysis of ATP by chloroplast ATP synthase, (b) that can result in an inhibited form of CF/sub 1/ that slowly regains activity during ATP hydrolysis, and (c) that arises when low concentrations of ADP markedly inhibit the hydrolysis of GTP by CF/sub 1/. The data show that in all instances the inhibition is associated with ADP binding without inorganic phosphate (P/sub i/) at catalytic sites. After photophosphorylation of ADP or 2-azido-ADP with (/sup 32/P)P/sub i/, similar amounts of the corresponding triphosphates are present on washed thylakoid membranes. Trials with appropriately labeled substrates show that a small portion of the tightly bound 2-azido-ATP gives rise to covalent labeling with an ATP moiety at noncatalytic sites but that most of the bound 2-azido-ATP gives rise to covalent labeling with an ATP moiety at noncatalytic sites but that most of the bound 2-azido-ATP gives rise to covalent labeling by an ADP moiety at a catalytic site. They also report the occurrence of a 1-2-min delay in the onset of the Mg/sup 2 +/-induced inhibition after addition of CF/sub 1/ to solutions containing Mg/sup 2 +/ and ATP, and that this delay is not associated with the filling of noncatalytic sites. A rapid burst of P/sub i/ formation is followed by a much lower, constant steady-state rate. The burst is not observed with GTP as a substrate or with Ca/sup 2 +/ as the activating cation.
- Research Organization:
- Univ. of California, Los Angeles (USA)
- DOE Contract Number:
- AS03-76ER70102
- OSTI ID:
- 7188223
- Journal Information:
- Biochemistry; (United States), Vol. 27:14
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ATP-ASE
BIOCHEMISTRY
NUCLEOTIDES
ENZYMATIC HYDROLYSIS
ATP
AZIDO COMPOUNDS
CATIONS
CHLOROPLASTS
LIGASES
MAGNESIUM COMPOUNDS
PHOSPHORUS 32
PHOSPHORYLATION
ACID ANHYDRASES
ALKALINE EARTH METAL COMPOUNDS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CELL CONSTITUENTS
CHARGED PARTICLES
CHEMICAL REACTIONS
CHEMISTRY
DAYS LIVING RADIOISOTOPES
DECOMPOSITION
ENZYMES
HYDROLASES
HYDROLYSIS
IONS
ISOTOPES
LIGHT NUCLEI
LYSIS
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOSPHOHYDROLASES
PHOSPHORUS ISOTOPES
RADIOISOTOPES
SOLVOLYSIS
550201* - Biochemistry- Tracer Techniques