ATP synthase of chloroplast thylakoid membranes: a more in depth characterization of its ATPase activity

In contrast to everted mitochondrial inner membrane vesicles and eubacterial plasma membrane vesicles, the ATPase activity of chloroplast ATP synthase in thylakoid membranes is extremely low. Several treatments of thylakoids that unmask ATPase activity are known. Illumination of thylakoids that contain reduced ATP synthase (reduced thylakoids) promotes the hydrolysis of ATP in the dark. Incubation of thylakoids with trypsin can also elicit higher rates of ATPase activity. In this paper the properties of the ATPase activity of the ATP synthase in thylakoids treated with trypsin are compared with those of the ATPase activity in reduced thylakoids. The trypsin-treated membranes have significant ATPase activity in the presence of Ca2+, whereas the Ca2+-ATPase activity of reduced thylakoids is very low. The Mg2+-ATPase activity of the trypsinized thylakoids was only partially inhibited by the uncouplers, at concentrations that fully inhibit the ATPase activity of reduced membranes. Incubation of reduced thylakoids with ADP in Tris buffer prior to assay abolishes Mg2+-ATPase activity. The Mg2+-ATPase activity of trypsin-treated thylakoids was unaffected by incubation with ADP. Trypsin-treated membranes can make ATP at rates that are 75-80% of those of untreated thylakoids. The Mg2+-ATPase activity of trypsin-treated thylakoids is coupled to inward proton translocation and 10 mM sulfite stimulates both proton uptake and ATP hydrolysis. It is concluded that cleavage of the gamma subunit of the ATP synthase by trypsin prevents inhibition of ATPase activity by the epsilon subunit, but only partially overcomes inhibition by Mg2+ and ADP during assay.

Harmonic response of cellular membrane pumps to low frequency electric fields

We report on harmonic generation by budding yeast cells in response to a sinusoidal electric field, which is seen to be minimal when the field amplitude is less than a threshold value. Surprisingly, sodium metavanadate, an inhibitor of P-type ATPases reportedly responsible for nonlinear response in yeast, reduces the threshold field amplitude, increasing harmonic generation at low amplitudes while reducing it at large amplitudes, whereas the addition of glucose dramatically increases the production of even harmonics. Finally, a simple model is proposed to interpret the observed behavior.

Proteasome structures affected by ionizing radiation

Exposure of cells to ionizing radiation slows the rate of degradation of substrates through the proteasome. Because the 26S proteasome degrades most short-lived cellular proteins, changes in its activity might significantly, and selectively, alter the life span of many signaling proteins and play a role in promoting the biological consequences of radiation exposure, such as cell cycle arrest, DNA repair, and apoptosis. Experiments were therefore undertaken to identify the radiation target that is associated with the proteasome. Regardless of whether they were irradiated before or after extraction and purification from human prostate cancer PC3 cells, 26S proteasomes remained intact but showed a rapid 30% to 50% dose-independent decrease in their three major enzymatic activities following exposure to 1 to 20 Gy. There was no effect on 20S proteasomes, suggesting that the radiation-sensitive target is located in the 19S cap of the 26S proteasome, rather than in the enzymatically active core. Because the base of the 19S cap contains an ATPase ring that mediates substrate unfolding, pore opening, and translocation of substrates into the catalytic chamber, we examined whether the ATPase activity of purified 26S proteasomes was affected. In fact, in vitro irradiation of proteasomes enhanced their ATPase activity. Furthermore, pretreatment with low concentrations of the free radical scavenger tempol was able to prevent both the radiation-induced decrease in proteolytic activity and the increase in ATP utilization, indicating that free radicals are mediators of these radiation-induced phenomena. Finally, we have shown that cell irradiation results in the accumulation of proteasome substrates: polyubiquitinated proteins and ornithine decarboxylase, indicating that the observed decrease in proteasome function is physiologically relevant.

[Effects of UV-radiation on metabolism and structural-functional status of the rat's erythrocyte membranes]

In-vitro analysis of venous blood taken from rats irradiated by 300 and 5,000 J/m2 of UV showed no effect on metabolism and, therefore, energy and recovery systems of erythrocytes. Concentrations of 2,3-diphosphoglycerate and reduced glutathione were increased after irradiation by 5,000 J/m2. UV-irradiation at 10,000 J/m2 decreased adenosine triphosphate and phospholipids in blood and impaired the functional stability of erythrocyte membranes. Recovery of the membrane structure in 24 hrs. after irradiation suggests extended photochemical processes in cells and is consistent with the literary data about indirect effects of plasma proteins on the red cell function.

Dietary selenium levels determine epidermal langerhans cell numbers in mice

Selenium (Se) is a dietary trace element that is essential for effective immunity and protection from oxidative damage induced by ultraviolet radiation (UVR). Langerhans cells (LC) represent the major antigen-presenting cells resident in the epidermis; a proportion migrate from the skin to the draining lymph nodes in response to UVR. Because it is known that Se deficiency impairs immune function, we determined what effect this has on LC numbers. CH3/HeN mice were weaned at 3 wk and placed on diets containing <0.005 ppm of Se (Se deficient) or 0.1 ppm of Se (Se adequate, control mice). After 5 wk on the diet, the epidermal LC numbers in the Se-adequate group were 966 +/- 51 cells/mm2 and LC counts in the epidermis of the Se-deficient mice were 49% lower (p<0.05). Glutathione peroxidase- I (GPx) activity was measured in the epidermis, lymph nodes, and liver. In the epidermis, the activity of GPx in the Se-deficient mice was only 39% (p<0.01) of that seen in epidermis from Se-adequate mice (1.732 U/mg protein). The mice were then irradiated with one dose of 1440 J/m2 of broadband UVB or mock irradiated. After 24 h, the decrease in LC number after UVB was greater in the Se-adequate mice, (40% decrease) compared to the Se-deficient group (10%). Thus, Se deficiency reduces epidermal LC numbers, an effect that might compromise cutaneous immunity.

Blue light inactivates plasma membrane H(+)-ATPase in pulvinar motor cells of Phaseolus vulgaris L

Unilateral blue light irradiation induces bending of pulvini of Phaseolus vulgaris towards the source of light. The pulvinar bending is caused by a decrease in turgor pressure of motor cells that are irradiated with blue light. Decrease in the turgor pressure is caused by the net efflux of K(+) and counter anions, accompanying membrane depolarization. In the present study the effect of blue light on the activity of plasma membrane H(+)-ATPase was studied in relation to the membrane depolarization. The activity of the plasma membrane H(+)-ATPase was measured using protoplast suspensions prepared from laminar pulvini from primary leaves. A pulse of blue light under continuous red light irradiation induced both a transient increase in the external pH and transient inhibition of the vanadate-sensitive ATPase. Continuous blue light irradiation under continuous red light irradiation induced both a sustained increase in the external pH and sustained inhibition of the vanadate-sensitive ATPase. These results show that blue light inhibits the activity of the plasma membrane H(+)-ATPase. Inactivation of the plasma membrane H(+)-ATPase supports the membrane depolarization induced by the blue light irradiation.

Dephosphorylation and subcellular compartment change of the mitotic Bloom's syndrome DNA helicase in response to ionizing radiation

Bloom's syndrome is a rare human autosomal recessive disorder that combines a marked genetic instability and an increased risk of developing all types of cancers and which results from mutations in both copies of the BLM gene encoding a RecQ 3'-5' DNA helicase. We recently showed that BLM is phosphorylated and excluded from the nuclear matrix during mitosis. We now show that the phosphorylated mitotic BLM protein is associated with a 3'-5' DNA helicase activity and interacts with topoisomerase III alpha. We demonstrate that in mitosis-arrested cells, ionizing radiation and roscovitine treatment both result in the reversion of BLM phosphorylation, suggesting that BLM could be dephosphorylated through the inhibition of cdc2 kinase. This was supported further by our data showing that cdc2 kinase activity is inhibited in gamma-irradiated mitotic cells. Finally we show that after ionizing radiation, BLM is not involved in the establishment of the mitotic DNA damage checkpoint but is subjected to a subcellular compartment change. These findings lead us to propose that BLM may be phosphorylated during mitosis, probably through the cdc2 pathway, to form a pool of rapidly available active protein. Inhibition of cdc2 kinase after ionizing radiation would lead to BLM dephosphorylation and possibly to BLM recruitment to some specific sites for repair.

Importance of heptameric ring integrity for activity of Escherichia coli ClpP

Radiation target analysis has been used to identify the minimal functional unit for expression of activity of ClpP, the proteolytic component of the ATP-dependent ClpAP protease. Radiation target sizes determined for small peptide hydrolysis, for ClpA activated and nucleotide-activated oligopeptide cleavage, and for ClpA-activated ATP-dependent protein degradation were 154, 118, and 160 kDa, respectively. Thus, the hydrolytic activity of ClpP, subunit M, 21,500, is dependent on the native oligomeric structure. The quaternary structure of ClpP determined by electron microscopy and hydrodynamic studies consists of two face-to-face seven-membered rings. The radiation target sizes are consistent with a requirement for conformational integrity of an entire ring for expression of hydrolytic activity. Radiation damage led to disruption of inter-ring contacts, giving rise to isolated rings of ClpP. Thus, contacts between rings of ClpP are less stable and more easily disrupted than contacts between subunits within the rings. Our data suggest that cooperative interactions between subunits within the ClpP rings are important for maintaining the active conformation of the proteolytic active site.

SOS induction by gamma-radiation in Escherichia coli strains defective in repair and/or recombination mechanisms

Ionizing radiation causes several types of DNA lesions, mainly single- or double-strand breaks and base damage. By means of the chromotest, an assay that allows the level of the SOS response to be monitored via beta-galactosidase enzymatic activity, the roles of several repair (uvrA, recN and oxyR) and recombination (recB, recJ and recO) genes in the response of Escherichia coli to gamma-radiation were studied. The results indicate that all the repair- and recombination-deficient strains were more sensitive to the lethal effects of ionizing radiation. However, the SOS activation pattern was somewhat different. The minimal inducing dose in uvrA and recN mutants was lower than in the wild-type, whereas their SOS response was higher at all doses. Conversely, in the strains lacking an active recB, recJ or recO gene, the doubling dose was almost the same as in the wild-type but the level of induction remained stable over a wide dose range. These findings suggest that neither single- nor double-strand breaks are in themselves direct SOS inducers and that while uvrA, recN and oxyR take part in different repair or protective pathways, apparently recB, recJ and recO participate in damage processing leading to SOS induction, as well as in recombination repair.

[The acute action of gamma radiation at a dose of 1 Gy on the enzymatic activity of serum ATPase and ADPase]

Studies were carried out to investigate the activity of ATPase and ADPase in rat blood serum after strong (137Cs) on the rate of 1 Gy. Rats were examined for various postirradiation periods up to 3 months. Two-fold decreasing of serum ATPase activity was recorded within the two weeks after gamma-irradiation. The rate of 3H-ADP enzymatic hydrolysis in the serum of irradiated animals remained unchanged as compared to controls.

The low-affinity ATP binding site of the Escherichia coli SecA dimer is localized at the subunit interface

The homodimeric SecA protein is the ATP-dependent force generator in the Escherichia coli precursor protein translocation cascade. SecA contains two essential nucleotide binding sites (NBSs), i.e., NBS1 and NBS2 that bind ATP with high and low affinity, respectively. The photoactivatable bifunctional cross-linking agent 3'-arylazido-8-azidoadenosine 5'-triphosphate (diN3ATP) was used to investigate the spatial arrangement of the nucleotide binding sites of SecA. DiN3ATP is an authentic ATP analogue as it supports SecA-dependent precursor protein translocation and translocation ATPase. UV-induced photo-cross-linking of the diN3ATP-bound SecA results in the formation of stable dimeric species of SecA. D209N SecA, a mutant unable to bind nucleotides at NBS1, was also photo-cross-linked by diN3ATP, whereas no cross-linking occurred with the NBS2 mutant R509K SecA. We concluded that the low-affinity NBS2, which is located in the carboxyl-terminal half of SecA, is the site of crosslinking and that NBS2 binds nucleotides at or near the subunit interface of the SecA dimer.

Conserved motifs II to VI of DNA helicase II from Escherichia coli are all required for biological activity

There are seven conserved motifs (IA, IB, and II to VI) in DNA helicase II of Escherichia coli that have high homology among a large family of proteins involved in DNA metabolism. To address the functional importance of motifs II to VI, we employed site-directed mutagenesis to replace the charged amino acid residues in each motif with alanines. Cells carrying these mutant alleles exhibited higher UV and methyl methanesulfonate sensitivity, increased rates of spontaneous mutagenesis, and elevated levels of homologous recombination, indicating defects in both the excision repair and mismatch repair pathways. In addition, we also changed the highly conserved tyrosine(600) in motif VI to phenylalanine (uvrD309, Y600F). This mutant displayed a moderate increase in UV sensitivity but a decrease in spontaneous mutation rate, suggesting that DNA helicase II may have different functions in the two DNA repair pathways. Furthermore, a mutation in domain IV (uvrD307, R284A) significantly reduced the viability of some E. coli K-12 strains at 30 degrees C but not at 37 degrees C. The implications of these observations are discussed.

Mutation of a highly conserved arginine in motif IV of Escherichia coli DNA helicase II results in an ATP-binding defect

A site-directed mutation in motif IV of Escherichia coli DNA helicase II (UvrD) was generated to examine the functional significance of this region. The highly conserved arginine at position 284 was replaced with alanine to construct UvrD-R284A. The ability of the mutant allele to function in methyl-directed mismatch repair and UvrABC-mediated nucleotide excision repair was examined by genetic complementation assays. The R284A substitution abolished function in both DNA repair pathways. To identify the biochemical defects responsible for the loss of biological function, UvrD-R284A was purified to apparent homogeneity, and its biochemical properties were compared with wild-type UvrD. UvrD-R284A failed to unwind a 92-base pair duplex region and was severely compromised in unwinding a 20-base pair duplex region. The Km of UvrD-R284A for ATP was significantly greater than 3 mM compared with 80 microM for UvrD. A large decrease in ATP binding was confirmed using a nitrocellulose filter binding assay. These data suggested that the R284A mutation severely reduced the affinity of helicase II for ATP. The reduced unwinding activity and loss of biological function of UvrD-R284A was probably the result of decreased affinity for ATP. These results implicate motif IV of superfamily I helicases in nucleotide binding and represent the first characterization of a helicase mutation outside motifs I and II that severely impacted the Km for ATP.

Structure-function relationships in Escherichia coli transcription termination protein Rho revealed by radiation target analysis

High-energy electrons were used to measure the target sizes for inactivation of the RNA-dependent ATPase activity of Escherichia coli transcription termination factor Rho, for its ATP binding ability, and for its physical destruction. SDS-PAGE analysis of irradiated samples indicated that the target size for polypeptide destruction in the homohexameric enzyme is the dimer, indicating that energy transfer must occur from a hit subunit to one other subunit, although the subunits are not known to be linked by any covalent bonds. The ATP binding ability of Rho also inactivates as a dimer, a result that is consistent with the physical destruction target size. However, a single subunit as the ATP binding entity is not excluded. The RNA-dependent ATPase activity of Rho inactivates with the apparent target size of trimer to tetramer, indicating that interactions among the subunits of Rho are required for ATP hydrolysis. Rho hexamers are known to exchange subunits, although the identity of the exchanging unit is not known. Models in which this property of Rho is taken into account indicate that the closest fit to the experimental data is for an ATPase target size of a hexamer with dimers as the exchanging units, consistent with earlier chemical inactivation studies.

Effects of static magnetic field on specific adenosine-5'- triphosphatase activities and bioelectrical and biomechanical properties in the rat diaphragm muscle

In this study, we aimed to clarify the effects of chronically applied static magnetic field (200 Gauss) on specific ATPase activities and bioelectrical and biomechanical responses in isolated rat diaphragm muscle. The mean activities of Na(+)-K+ ATPase and Ca2+ ATPase determined from the diaphragm homogenates were significantly higher in the magnetic field exposed group (n = 20), but that of Mg2+ ATPase was nonsignificantly lower compared to the control group (n = 13). Resting membrane potential, amplitude of muscle action potential, and overshoot values (mean +/- SE) in the control group were found to be -76.5 +/- 0.6, 100 +/- 0.8, and 23.5 +/- 0.6 mV, respectively; these values were determined to be -72.8 +/- 0.4, 90.3 +/- 0.5, and 17.2 +/- 0.4 mV in the magnetic field-exposed group, respectively. The latency was determined to increase in the experimental group, and all the above-mentioned bioelectrical differences between the groups were significant statistically. Force of muscle twitch was found to decrease significantly in the magnetic field-exposed group, and this finding was attributed to the augmenting effect of magnetic field on Ca2+ ATPase activity. These results suggest that magnetic field exposure changes specific ATPase activities and, thence, bioelectrical and biomechanical properties in the rat diaphragm muscle.

8-Azido-adenine nucleotides as substrates of ecto-nucleotidases in chromaffin cells: inhibitory effect of photoactivation

The components of the ecto-nucleotidase pathway at the extracellular surface of adrenal chromaffin cells are the enzymatic activities responsible for the hydrolysis of granular nucleotide compounds released during the secretory response. The azido-nucleotides have been largely employed to characterize nucleotide binding sites. The 8-azido-adenine nucleotides were studied as substrates of ecto-nucleotidases in cultured chromaffin cells by HPLC procedures. 8-Azido-ATP (8-N3-ATP) was a good substrate for ecto-ATPase activity, the Km value was 256.30 +/- 36.41 microM, and the Vmax value was 14.33 +/- 0.84 nmol/min x 10(6) cells. 8-Azido-ADP (8-N3-ADP) was dephosphorylated by the ecto-ADPase activity with a Km value of 595.29 +/- 67.44 microM and Vmax value of 6.86 +/- 0.45 nmol/min x 10(6) cells. These kinetic parameters were similar to those obtained with ATP and ADP in the same culture and incubation conditions. 8-Azido-AMP (8-N3-AMP) was not hydrolyzed by the ecto-5'-nucleotidase activity. The 8-azido-nucleotides competitively inhibited the hydrolysis of adenine nucleotides, with Ki values in the same range as the Km. After uv photoactivation, the three 8-azido-nucleotides (100 microM) irreversibly inhibited and to a similar extent, between 40 and 55%, each of ecto-nucleotidase activities. UV photoactivation in the presence of nucleotides in the same concentration range was an effective protection from the inhibition.

ATPase of Rhodospirillum rubrum requires three functional copies of beta subunit as determined by radiation inactivation analysis

Radiation inactivation analysis yielded a functional unit of 170 +/- 26 kDa as beta subunit of ATPase was irradiated and then reconstituted to beta-depleted chromatophores of Rhodospirillum rubrum. A functional size of 132 +/- 17 kDa for the beta-depleted ATPase moiety involved in ATP hydrolysis reaction was also determined. When both purified beta subunit and beta-depleted chromatophore were irradiated separately, reconstituted, and then activity measured, the functional mass was 312 +/- 50 kDa. Our compelling evidence directly indicates that three functional copies of beta subunits were required for ATP hydrolysis.

[The effect of laser irradiation of the blood on the adenosine triphosphatase activity of the erythrocyte membranes and on the cardiac activity indices in patients with ischemic heart disease]

The activity of potassium, sodium, magnesium and Ca-ATP-ase of the erythrocytic membrane, index of erythrocyte deformability, changes of the hemodynamics and some cardiac function during bicycle ergometry [correction of veloergometry] tests before and after a course of laser irradiation of the blood were studied in 36 patients with exertion stenocardia. It was established that laser therapy is accompanied by increase of the activity of ATP-ase, index of erythrocyte deformability and positive changes of the cardial function. The possibility is discussed of improving the cardiac function under the effect of laser irradiation as a result of optimization of the structural-functional organization of the cellular membrane.

Characterization of Escherichia coli SecA protein binding to a site on its mRNA involved in autoregulation

In order to understand further the autogenous regulation of Escherichia coli secA translation, we have set up a purified system to study the binding of SecA protein to portions of its mRNA. Specific SecA protein-RNA binding was demonstrated by UV cross-linking, filter binding, and gel shift assays. Use of the filter binding assay allowed optimization of binding, which was influenced by Mg2+ and ATP concentrations, and a measurement of the affinity of this interaction. A nested series of RNAs lacking either 5' or 3' portions of geneX-secA sequences were used to localize the SecA protein binding site to sequences around the geneX-secA intergenic region. These studies imply that SecA protein directly regulates its own translation by a specific RNA binding activity that presumably blocks translational initiation.

Microwave effect upon chlorpromazine-inhibited kidney ATPase

Presence of chlorpromazine, a non-active-site inhibitor of Na(+)-K(+)-ATPase catalytic activity, in a reaction system exposed to 9.14 GHz CW radiation, resulted in approximately 23% inhibition. This effect was temperature-independent within the normal range for this protein. A low-level microwave field also inhibited the enzyme catalytic rate. Loci of chlorpromazine inhibition and of low-level microwave inhibition appear to be distinct and non-interactive under the conditions of this study. Use of enzyme reaction systems as models for microwave causation of leukemia and the possible involvement of pharmacological agents, such as ouabain and chlorpromazine, in this process has been considered.

Results of a United States and Soviet Union joint project on nervous system effects of microwave radiation

During the course of a formal program of cooperation between the United States and the Soviet Union concerning the biological effects of physical factors in the environment, it was concluded that duplicate projects should be initiated with the general goal of determining the most sensitive and valid test procedures for evaluating the effects of microwave radiation on the central nervous system. This report details an initial step in this direction. Male rats of the Fischer 344 strain were exposed or sham exposed to 10 mW/cm2 continuous wave microwave radiation at 2.45 GHz for a period of 7 hr. Animals were subjected to behavioral, biochemical, or electrophysiological measurements during and/or immediately after exposure. Behavioral tests used were passive avoidance and activity in an open field. Biochemical measurements were ATPase (Na+, K+; Mg2+, Ca2+) and K+ alkaline phosphatase activities. Electrophysiological measurements consisted of EEG frequency analysis. Neither group observed a significant effect of microwave irradiation on open field activity. Both groups observed changes in variability of the data obtained using the passive avoidance procedure, but not in the same parameters. The U.S. group, but not the USSR group, found significantly less Na+,K+-ATPase activity in the microwave-exposed animals compared to the sham exposed animals. Both groups found incidences of statistically significant effects in the power spectral analysis of EEG frequency, but not at the same frequency. The failure of both groups to substantiate the results of the other reinforces our contention that such duplicate projects are important and necessary.

In vitro photosensitization of tumour cell enzymes by photofrin II administered in vivo

The ability of injected Photofrin II, a preparation enriched in hydrophobic dihaematoporphyrin ethers and esters, to photosensitize selected mitochondrial and cytosolic enzymes during illumination in vitro was examined. Preparations of R3230AC mammary tumours, obtained at designated times after a single dose of Photofrin II, displayed a time-dependent photosensitivity. Maximum inhibition of mitochondrial enzymes occurred at 24 hours post-treatment, whereas no inhibition of the cytosolic enzyme, pyruvate kinase, was observed over the 168 hour time course. At the selected 24 hour time point, mitochondrial enzyme photosensitisation was found to be drug dose (5.25 mg kg-1 Photofrin II) and light dose dependent, the rank order of inhibition being cytochrome c oxidase greater than F0F1 ATPase greater than succinate dehydrogenase greater than NADH dehydrogenase. We conclude that porphyrin species contained in Photofrin II accumulate in mitochondria of tumour cells in vivo and produce maximum photosensitisation at 24-72 hours after administration to tumour-bearing animals. The time course observed here with Photofrin II is similar to that seen previously with the more heterogenous haematoporphyrin derivative preparation in this in vivo-in vitro model.

Radiation inactivation analysis of oligomeric structure of the H,K-ATPase

The oligomeric size of the H,K-ATPase was determined in frozen gastric microsomal vesicles irradiated with high energy electrons. Target sizes of various catalytic activities associated with H,K-ATPase function fell into two distinct groups. The lower group of target sizes described the radiation-induced loss of steady-state phosphoenzyme and structural monomer: the MgATP-dependent formation of a beta-aspartyl phosphate exhibited a size range of 133-147 kDa; the size range for the structural measurement (i.e. loss of H,K-ATPase monomer on sodium dodecyl sulfate-polyacrylamide gels) was 92-143 kDa. In contrast, a larger group of target sizes described the loss of full cycle catalytic activities (i.e. K+-dependent stimulation of p-nitrophenyl phosphate and ATP hydrolysis). The K+-phosphatase and K+-stimulated ATPase exhibited target sizes fo 200 +/- 13 and 232 +/- 23 kDa, respectively. The lower target size group represents the first evidence that a monomer of the catalytic subunit maintains partial enzyme function. The larger group of target sizes describing K+-phosphatase and ATPase activities suggest that subunit interactions contribute to full cycle catalytic activity. Subunit interactions appear to be involved in all ion transport activities. Passive Rb+ exchange and active H+ transport in reconstituted proteoliposomes exhibited target sizes of 233n = 2 and 388 +/- 48 kDa, respectively. H+ transport appears to require a subunit arrangement more complex than that associated with catalytic activity or passive ion transport.

Vanadate-sensitized cleavage of dynein heavy chains by 365-nm irradiation of demembranated sperm flagella and its effect on the flagellar motility

Irradiation of demembranated flagella of sea urchin sperm at 365 nm in the presence of 0.05-1 mM MgATP and 5-10 microM vanadate (Vi) cleaves the alpha and beta heavy chains of the outer arm dynein at the same site and at about the same rate as reported previously for the solubilized dynein (Gibbons, I. R., Lee-Eiford, A., Mocz, G., Phillipson, C. A., Tang, W.-J. Y., and Gibbons, B. H. (1987) J. Biol. Chem. 262, 2780-2786). The decrease in intact alpha and beta heavy chain material is biphasic, with about 80% being lost with a half-time of 8-10 min, and the remainder more slowly. Five other axonemal polypeptides of Mr greater than 350,000 are lost similarly, concomitant with the appearance of at least 9 new peptides of Mr 150,000-250,000. The motility of irradiated sperm flagella upon subsequent dilution into reactivation medium containing 1 mM ATP and 2.5 mM catechol shows a progressive decrease in flagellar beat frequency for irradiation times that produce up to about 50% cleavage of the dynein heavy chains; more prolonged irradiation causes irreversible loss of motility. Competition between photocleaved and intact outer arm dynein for rebinding to dynein-depleted sperm flagella shows that cleavage has little effect upon the ability for rebinding, although the cleaved dynein partially inhibits subsequent motility. Substitution of MnATP for the MgATP in the irradiation medium prevents the loss of all of the axonemal polypeptides during irradiation for up to 60 min and also protects the potential for subsequent flagellar motility. It is concluded that loss of the five axonemal polypeptides upon irradiation results from a Vi-sensitized photocleavage similar to that which occurs in the alpha and beta heavy chains of outer arm dynein and that these polypeptides represent Vi-inhibitable ATPase subunits of dyneins located in the inner arms and possibly elsewhere in the flagellar axoneme.

[Radiation modification of the ATPase properties of submitochondrial particles]

The appreciable changes in hydrophobic properties of ATPase of rat liver submitochondrial particles were discovered 3 days after whole-body X-irradiation with a dose of 7 Gy. The sensitivity of ATPase activity to stimulating anions decreased. The radiation damages to ATPase were detected and the ratio of concentrations of magnesium and ATP exceeded a unity.

Specific cleavage of dynein heavy chains by ultraviolet irradiation in the presence of ATP and vanadate

Irradiation of soluble dynein 1 from sea urchin sperm flagella at 254 nm in the presence of 50 microM ATP and 100 microM inorganic vanadate (Vi) cleaves the alpha and beta heavy chains into approximately equal quantities of two polypeptides of Mr 228,000 and 200,000, with a conversion efficiency of about 63%. A similar cleavage occurs in the presence of Vi and either ADP or 8-azidoadenosine 5'-triphosphate (8-N3ATP); in the latter case, 8-N3ATP becomes covalently bound principally to the Mr 228,000 polypeptide. No detectable amount of these fragments is formed if either the Vi or the nucleotide is omitted or in the presence of Vi and 50 microM AMP. These results emphasize the basic similarity of the two ATPases associated with the alpha and beta heavy chain subunits of dynein 1 and give a mean Mr of 428,000 for the intact heavy chains.

ATPase and morphologic changes induced by UVB on Langerhans cells in guinea pigs

We have devised, in guinea pigs, an improved ATPase technique which enables one to proceed from light to electron microscope study while preserving, on the ultrastructural level, the various membranous structures, in particular the Langerhans cell (LC) granules. Using this method, we have been able to confirm the action of acute, low-dose UVB on the surface enzymatic marker, ATPase. Moreover, this study has shown that the ATPase-negative LC contain abnormal LC granules or, more often, are deficient in LC granules. In a previous work, we have shown that, after epicutaneous application of a hapten, one successively observes an extensive adsorptive pinocytosis process, the disappearance of the membranous ATPase system, and the appearance of LC granules in the cytoplasm. Therefore we may suppose that, after UVB irradiation, the disappearance of the ATPase system and/or the possible alteration of the adsorptive pinocytosis process interrupts or alters the formation of LC granules. These successive events might play a vital role in the formation of the hapten--carrier protein-Ia antigen complex. In their absence in a large number of LC, following UV irradiation, epicutaneous application of a hapten would lead to the development of a state of immune tolerance.

Target sizes of human erythrocyte membrane Ca2+-ATPase and Mg2+-ATPase activities in the presence and absence of calmodulin

We have investigated the subunit structure of Ca2+-transport ATPase in human erythrocyte membranes using radiation inactivation analysis. All inactivation data were linear on a semilog plot down to at least 20% of the control activity. We found a target size for the calmodulin-dependent Ca2+-ATPase activity of 331 kDa, consistent with the presence of this enzyme as a dimer in calmodulin-depleted ghosts. Membranes which had been saturated with calmodulin before irradiation yield a a similar size of 317 kDa, implying that activation of Ca2+-transport ATPase by calmodulin does not involve significant change in oligomeric structure. Basal (calmodulin-independent) Ca2+-ATPase activity corresponded to a size of 290 kDa, suggesting that this activity resides in the same, or similar-sized, complex as the calmodulin-dependent activity. Mg2+-ATPase activity, however, was found to reside in a smaller complex of 224 kDa, which proved to be statistically distinct from the target size of Ca2+-ATPase activity. It would appear that Mg2+-ATPase is a distinct entity whose function is likely unrelated to the Ca2+-transport ATPase.

Photosensitization of mitochondrial adenosine-triphosphatase and adenylate kinase by hematoporphyrin derivative in vitro

Mitochondrial ATPase and adenylate kinase activity of hepatoma cells were inhibited by hematoporphyrin derivative (HPD) followed by photoirradiation. Inhibition of ATPase activity was a dose- and time-related event. Malonaldehyde (MDA) content of mitochondrial membranes was markedly increased by HPD plus light. The content of mouse liver microsomal cytochrome P-450 was greatly increased after intraperitoneal injection of HPD for 4 days (5 mg/kg/day). The liver weight, and levels of liver microsomal G-6-phosphatase, MDA and triglyceride (TG) showed no difference in treated vs. control animals. The data presented here demonstrate that mitochondria may be a sensitive site of action of HPD photosensitization, and inactivation of ATPase and adenylate kinase may be an important contributing factor to tumor cell damage and death.

[Effect of changes in the lipids of mitochondrial membranes on the activity of Mg2+-dependent ATPase]

The results obtained permit to assume that irradiation causes dysfunction of the regulatory system that provides the interdependence between the antioxidative activity of lipids, their composition and the activity of membrane-bound enzymes. There is virtually no correlation between the changes in hydrolase activity of the enzyme and the quantity of phosphatidylethanolamine (PE) and cardiolipin (CL). During the first hours following irradiation the dependence between the changes in the synthetase activity of ATPase and the fluidity of the lipid component of the membrane is directly proportional (just as it is observed in normal conditions); the lesser the fluidity of the lipid component the higher the hydrolase activity of the enzyme.

[Changes in the mitochondrial ATPase activity of liver cells after X-ray irradiation]

24 h following total-body X-irradiation of rats with a dose of 7 Gy the growth of the ATPase activity diminished, with the addition of bicarbonate, by 2 times in the preparations of mitochondria and submitochondrial particles, and by 1.5 times, in preparations of a soluble enzyme. No changes were noted in the electrophoretic motility of soluble ATPase.

Inactivation of mitochondrial ATPase by ultraviolet light

The present work describes experiments that show that far-ultraviolet irradiation induce the inhibition of ATPase activity in both membrane-bound and soluble F1. It was also found that ultraviolet light promotes the release of tightly bound adenine nucleotides from F1-ATPase. Experiments carried out with submitochondrial particles indicate that succinate partially protects against these effects of ultraviolet light. Titration of sulfhydryl groups in both irradiated submitochondrial particles and soluble F1-ATPase indicates that a conformational change induced by photochemical modifications of amino acid residues appears involved in the inactivation of the enzyme. Finally, experiments are described which show that the tyrosine residue located in the active site of F1-ATPase is modified by ultraviolet irradiation.

Modulation of oat mitochondrial ATPase activity by CA2+ and phytochrome

The activity of a Mg(2+)-dependent ATPase present in highly purified preparations of Avena mitochondria was photoreversibly modulated by red/far-red light treatments. These results were obtained either with mitochondria isolated from plants irradiated with white light prior to the extraction or with mitochondria isolated from unirradiated plants only when purified phytochrome was exogenously added to the reaction mixture. Red light, which converts phytochrome to the far red-absorbing form (Pfr) depressed the ATPase activity, and far-red light reversed this effect. Addition of exogenous CaCl2 also depressed the ATPase activity, and the kinetics of inhibition were similar to the kinetics of the Pfr effects on the ATPase. The calcium chelator, ethyleneglycol-bis(beta-amino-ethyl ether)-N,N' -tetraacetic acid, blocked the effects of both CaCl2 and Pfr on the ATPase. These results are consistent with the interpretation that Pfr promotes a release of Ca2+ from the mitochondrial matrix, thereby inducing an increase in the concentration of intermembranal and extramitochondrial Ca2+.

Studies on (K+ + H+)-ATPase. VI. Determination on the molecular size by radiation inactivation analysis

(1) A (K+ + H+)-ATPase containing membrane fraction, isolated from pig gastric mucosa, has been further purified by means of zonal electrophoresis, leading to a 20% increase in specific activity and an increase in ratio of (K+ + H+)-ATPase to basal Mg2+-ATPase activity from 9 to 20. (2) The target size of (Na+ + K+)-ATPase, determined by radiation inactivation analysis, is 332 kDa, in excellent agreement with the earlier value of 327 kDa obtained from the subunit composition and subunit molecular weights. This shows that the Kepner-Macey factor of 6.4 X 10(11) is valid for membrane-bound ATPases. (3) The target size of (K+ + H+)-ATPase is 444 kDa, which, in connection with a subunit molecular weight of 110000, suggests a tetrameric assembly of the native enzyme. The ouabain-insensitive K+-stimulated p-nitrophenylphosphatase activity has a target size of 295 kDa. (4) In the presence of added Mg2+ the target sizes of the (K+ + H+)-ATPase and its phosphatase activity are decreased by about 15%, while that for the (Na+ + K+)-ATPase is not significantly changed. This observation is discussed in terms of a Mg2+-induced tightening of the subunits composing the (K+ + H+)-ATPase molecule.

Target molecular weight of the gastric (H+ + K+)-ATPase functional and structural molecular size

The state of assembly of the (H+ + K+)-ATPase in purified hog gastric mucosa membranes was studied by target size analysis applied to radiation-induced enzyme inactivation and polypeptide degradation data. Radiation inactivated the Mg2+-ATPase, K+-stimulated ATPase, and p-nitrophenyl phosphatase activities of the membrane preparation with a dose dependence characteristic of a target size of 270,000-daltons. Radiation also bleached the major 100,000-dalton sodium dodecyl sulfate-gel electrophoresis band of this preparation, indicating a radiation-induced degradation. This apparent polypeptide degradation exhibited a dose dependency corresponding to a target size of 250,000 daltons in situ. It is suggested that the gastric ATPase is a trimeric assembly of the 100,000-dalton polypeptides.

Light-induced Mg2+ ATPase activity of coupling factor in intact chloroplasts

Intense illumination isolated, intact, spinach chloroplasts triggers the well known proton-pumping Mg2+ ATPase activity of coupling factor, which can be assayed in subsequently lysed chloroplasts by monitoring ATP-driven quenching of 9-aminoacridine fluorescence. The light-triggered ATPase activity decays slowing in the dark and is inhibited by N,N'-dicyclohexylcarbodiimide. After osmotic lysis and washing of the chloroplasts, preillumination no longer triggers maximal proton-pumping ATPase until methylviologen and dithiothreitol are added to the medium. It is suggested that intact organelles contain soluble or loosely bound cofactors necessary for light-triggering of coupling factor ATPase. On osmotic lysis, these endogenous cofactors are diluted or inactivated and must be replaced by addition of a dithiol reagent and an electron acceptor.

8-Azido-adenosine 5'-triphosphate as a photoaffinity label for bacterial F1 ATPase

1. 8-Azido-adenosine 5'-triphosphate (n83ATP) is a suitable photoaffinity label for F1 ATPase from Micrococcus luteus. The nucleotide is a substrate in the presence of bivalent cations and inhibits the enzyme irreversibly upon irradiation with ultraviolet light above 300 nm. 2. More than 80% of the label is covalently bound to the beta subunits in the presence of bivalent cations. Labeling and inactivation is decreased by protection with ADP, ATP or adenyl-5'-yl imidodiphosphate. To a much smaller degree the alpha subunits also become labeled. 3. n83AMP does not specifically bind to the beta subunits upon irradiation. Like n83ATP and n83ADP, it also labels the alpha subunits to a small extent. 4. The F1 ATPase is inactivated after a single beta subunit per F1 complex has become labeled. A cooperativity of the beta subunits carrying nucleotide binding sites is suggested.