Biomaterial Database

On the mechanism of sulfite activation of chloroplast thylakoid ATPase and the relation of ADP tightly bound at a catalytic site to the binding change mechanism. 1990

Z Y Du, and P D Boyer

Department of Chemistry and Biochemistry, University of California, Los Angeles 90024-1570.

Washed chloroplast thylakoid membranes upon exposure to [3H]ADP retain a tightly bound [3H]ADP on a catalytic site of the ATP synthase. The presence of sufficient endogenous or added Mg2+ results in an enzyme with essentially no ATPase activity. Sulfite activates the ATPase, and many molecules of ATP per synthase can be hydrolyzed before most of the bound [3H]ADP is released, a result interpreted as indicating that the ADP is not bound at a site participating in catalysis by the sulfite-activated enzyme [Larson, E. M., Umbach, A., & Jagendorf, A. T. (1989) Biochim. Biophys. Acta 973, 75-85]. We present evidence that this is not the case. The Mg2(+)- and ADP-inhibited enzyme when exposed to MgATP and 20-100 mM sulfite shows a lag of about 1 min at 22 degrees C and of about 15 s at 37 degrees C before reaching the same steady-state rate as attained with light-activated ATPase that has not been inhibited by Mg2+ and ADP. The lag is not eliminated if the enzyme is exposed to sulfite prior to MgATP addition, indicating that ATPase turnover is necessary for the activation. The release of most of the bound [3H]ADP parallels the onset of ATPase activity, although some [3H]ADP is not released even with prolonged catalytic turnover and may be on poorly active or inactive enzyme or at noncatalytic sites. The results are consistent with most of the tightly bound [3H]ADP being at a catalytic site and being replaced as this Mg2(+)- and ADP-inhibited site regains equivalent participation with other catalytic sites on the activated enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

UI	MeSH Term	Description	Entries
D008274	Magnesium	A metallic element that has the atomic symbol Mg, atomic number 12, and atomic weight 24.31. It is important for the activity of many enzymes, especially those involved in OXIDATIVE PHOSPHORYLATION.
D010944	Plants	Multicellular, eukaryotic life forms of kingdom Plantae. Plants acquired chloroplasts by direct endosymbiosis of CYANOBACTERIA. They are characterized by a mainly photosynthetic mode of nutrition; essentially unlimited growth at localized regions of cell divisions (MERISTEMS); cellulose within cells providing rigidity; the absence of organs of locomotion; absence of nervous and sensory systems; and an alternation of haploid and diploid generations. It is a non-taxonomical term most often referring to LAND PLANTS. In broad sense it includes RHODOPHYTA and GLAUCOPHYTA along with VIRIDIPLANTAE.	Plant
D002736	Chloroplasts	Plant cell inclusion bodies that contain the photosynthetic pigment CHLOROPHYLL, which is associated with the membrane of THYLAKOIDS. Chloroplasts occur in cells of leaves and young stems of plants. They are also found in some forms of PHYTOPLANKTON such as HAPTOPHYTA; DINOFLAGELLATES; DIATOMS; and CRYPTOPHYTA.	Chloroplast,Etioplasts,Etioplast
D004789	Enzyme Activation	Conversion of an inactive form of an enzyme to one possessing metabolic activity. It includes 1, activation by ions (activators); 2, activation by cofactors (coenzymes); and 3, conversion of an enzyme precursor (proenzyme or zymogen) to an active enzyme.	Activation, Enzyme,Activations, Enzyme,Enzyme Activations
D000244	Adenosine Diphosphate	Adenosine 5'-(trihydrogen diphosphate). An adenine nucleotide containing two phosphate groups esterified to the sugar moiety at the 5'-position.	ADP,Adenosine Pyrophosphate,Magnesium ADP,MgADP,Adenosine 5'-Pyrophosphate,5'-Pyrophosphate, Adenosine,ADP, Magnesium,Adenosine 5' Pyrophosphate,Diphosphate, Adenosine,Pyrophosphate, Adenosine
D000251	Adenosine Triphosphatases	A group of enzymes which catalyze the hydrolysis of ATP. The hydrolysis reaction is usually coupled with another function such as transporting Ca(2+) across a membrane. These enzymes may be dependent on Ca(2+), Mg(2+), anions, H+, or DNA.	ATPases,Adenosinetriphosphatase,ATPase,ATPase, DNA-Dependent,Adenosine Triphosphatase,DNA-Dependent ATPase,DNA-Dependent Adenosinetriphosphatases,ATPase, DNA Dependent,Adenosinetriphosphatases, DNA-Dependent,DNA Dependent ATPase,DNA Dependent Adenosinetriphosphatases,Triphosphatase, Adenosine
D000255	Adenosine Triphosphate	An adenine nucleotide containing three phosphate groups esterified to the sugar moiety. In addition to its crucial roles in metabolism adenosine triphosphate is a neurotransmitter.	ATP,Adenosine Triphosphate, Calcium Salt,Adenosine Triphosphate, Chromium Salt,Adenosine Triphosphate, Magnesium Salt,Adenosine Triphosphate, Manganese Salt,Adenylpyrophosphate,CaATP,CrATP,Manganese Adenosine Triphosphate,MgATP,MnATP,ATP-MgCl2,Adenosine Triphosphate, Chromium Ammonium Salt,Adenosine Triphosphate, Magnesium Chloride,Atriphos,Chromium Adenosine Triphosphate,Cr(H2O)4 ATP,Magnesium Adenosine Triphosphate,Striadyne,ATP MgCl2
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D013447	Sulfites	Inorganic salts of sulfurous acid.	Sulfite,Sulfites, Inorganic,Inorganic Sulfites