Adenine nucleotide binding sites on beef heart F1 ATPase: photoaffinity labeling of beta-subunit Tyr-368 at a noncatalytic site and beta Tyr-345 at a catalytic site.

Abstract

2-Azidoadenine [32P]nucleotide was bound specifically at catalytic or noncatalytic nucleotide binding sites on beef heart mitochondrial F. ATPase. In both cases, photolysis resulted in nearly exclusive labeling of the I8 subunit. The modified enzyme was digested with trypsin, and labeled peptides were purified by reversed-phase high-pressure liquid chromatography. Amino acid sequence analysis of the major 32P-labeled tryptic fragments showed 13-subunit Tyr-368 to be present at noncatalytic sites and /8 Tyr-345 to be present at catalytic sites. From the relationship between the degree of inhibition and extent of modification, it is estimated that one-third of the catalytic sites or two-thirds of the noncatalytic sites must be modified to give near-complete inhibition of catalytic activity.The ATP synthase FtFl, found in mitochondria, chloroplasts, and bacteria, couples proton translocation to ATP synthesis during oxidative phosphorylation and photophosphorylation. The F1 component can be readily solubilized and has a a3f33y&e subunit structure. F1 contains the catalytic sites for ATP synthesis, but when detached from the membrane it is only capable of net ATP hydrolysis (1, 2).Of the six nucleotide binding sites present on the beef heart mitochondrial enzyme, MF1, only three sites exchange bound nucleotide rapidly during hydrolysis of MgATP at pH 8.0 (3). Evidence has been presented that at least two (4-6) and probably all three (7-12) of the exchangeable sites participate sequentially in catalysis at high substrate concentration. The three nonexchangeable sites, referred to here as noncatalytic sites, have been suggested to play a structural or regulatory role (for example, see refs. 13 and 14).A valuable approach to the characterization of nucleotide binding sites on F1 has been the use of affinity and photoaffinity analogs (15). Perhaps the most promising probes are the 2-azidoadenine nucleotides (11,16,17). Their anti conformation resembles that of F1-bound ADP and ATP; thus, they bind very tightly and serve as good substrates (18). Procedures described by Kironde and Cross (19) Garin et al. (22). We also report here the effects of derivatization on catalytic activity. MATERIALS AND METHODSPreparation of MF1. MF1 was isolated from beef heart mitochondria as described (23) Photoaffinity Labeling. To label a noncatalytic nucleotide site, in a typical experiment 60 ,ul of 14.5 mM 2-azido-[,B,y-32P]ATP was added with rapid mixing to 450 ul of 75 ,uM MF1[2,1] and incubated for 15 min. Unbound ligand was removed on a 3-ml centrifuge column, and MgATP was added to a final concentration of 15 mM to displace 2-azido-ANP from catalytic sites. After 1 min, the enzyme was passed through a second 3-ml centrifuge column and diluted to 2 ml. Four 500-,ul aliquots were placed on a shallow plastic tray 8 mm from a Minerallight lamp and photolyzed at the short wavelength setting for 30 min.To 5715The publication costs of this article were defrayed in part by page charge payment. This article must therefore be here...

Rotary Movements within the ATP Synthase do not Constitute an Obligatory Element of the Catalytic Mechanism

“…Since the enzyme contains 3 a and 3 b sites, one of them is bound at an a site and one at a b site. Similar experiments were more recently performed with 2-azido-ADP (43), an analogue that has the same anti-configuration as ADP and of which the site of binding can be unequivocally determined by analysis of the site of modification after illumination (44,45). Also in this case 2 a sites and 2 b sites could be occupied with the analogue, while the two nonexchangeable nucleotides were still bound at their original sites (43), apparently one a site and one b site.…”

Guanosine and formycin triphosphates bind at non‐catalytic nucleotide binding sites of CF1 ATPase and inhibit ATP hydrolysis

“…The possibility of direct interaction needs consideration because 2-azido-ATP bound at catalytic or non-catalytic sites labels tyrosines only 25 residues apart [6,7,28] …”

The catalytic site is located on subunit I of the ATPase from Halobacterium saccharovorum

“…In addition, F l-ATPases contain three noncatalytic sites; these are also tight-binding sites with a high specificity for adenine nucleotides, but not exchangeable during catalysis [36 -381. Differential labeling after occupation of either catalytic or non-catalytic sites with radioactive 2-azido-ATP both led to the incorporation of the label into the jl subunit, but at two different positions on adjacent peptides [17][18][19]411. Labeling of the CI subunit was either minor or completely absent [19, 381. With photocross-linking experiments using the physiological substrate of the ATPase as the affinity label, we were able to identify at least two distinct types of nucleotide-binding sites on the H. saccharovorum ATPase.…”