Localization of a carboxylic residue possibly involved in the inhibition of vacuolar H+-pyrophosphatase by N, N'-dicyclohexylcarbodi-imide

A vacuolar H(+)-pyrophosphatase (EC 3.6.1.1) that catalyses PP(i) hydrolysis and the electrogenic translocation of protons from the cytosol to the vacuole lumen, was purified from etiolated hypocotyls of mung bean seedlings (Vigna radiata L.). Group-specific modification was used to identify a carboxylic residue involved in the inhibition of vacuolar H(+)-pyrophosphatase. Carbodi-imides, such as N,N'-dicyclohexylcarbodi-imide (DCCD) and 1-ethyl-3-(3-dimethylamino-propyl)carbodi-imide, and Woodward's reagent K caused a progressive decline in the enzymic activity of vacuolar H(+)-pyrophosphatase in a time- and concentration-dependent manner. The stoichiometry of labelling of the vacuolar H(+)-pyrophosphatase by [(14)C]DCCD determined that DCCD modifies one carboxylic residue per subunit of the enzyme. Protection studies suggest that the DCCD-reactive carboxylic residue resides at or near the substrate-binding site. Furthermore, peptide mapping analysis reveals that Asp(283), located in the putative loop V of a tentative topological model of vacuolar H(+)-pyrophosphatase on the cytosolic side, was labelled by radioactive [(14)C]DCCD. Cytosolic loop V contains both DCCD-sensitive Asp(283) and a conserved motif sequence, rendering it a candidate for the catalytic site of vacuolar H(+)-pyrophosphatase. A topological picture of the active domain of vacuolar H(+)-pyrophosphatase is tentatively proposed.

Improvement of beamline 4B9A and results of an X-ray diffraction experiment

4B9A is a focusing and monochromatic photon beam at the BSRF, which was constructed in 1990. During the second phase of the BSRF program, the surface of the cylindrical mirror has been coated with Pt, covering the original Ni, and the monochromator has been upgraded. The maximum photon energy extends to 11 keV and the intensity has increased about tenfold with respect to the previous intensity at 6 keV. Synchrotron X-ray diffraction patterns for the Hg-1223 (HgBa(2)Ca(2)Cu(3)O(8+delta)) superconducting bulk and thin film have been measured at 1.54014 A. Results indicate that the bulk and film can be indexed as possessing tetragonal symmetry; lattice parameters a = 3.856 A and c = 15.851 A for the bulk Hg-1223 compound, and a = 3.8517 A and c = 15.8511 A for the film. Their structures are similar.

Subunit interaction of vacuolar H+-pyrophosphatase as determined by high hydrostatic pressure

Vacuolar H+-pyrophosphatase (H+-PPase) from etiolated hypocotyls of mung bean (Vigna radiata L.) is a homodimer with a molecular mass of 145 kDa. The vacuolar H+-PPase was subjected to high hydrostatic pressure to investigate its structure and function. The inhibition of H+-PPase activity by high hydrostatic pressure has a pressure-, time- and protein-concentration-dependent manner. The Vmax value of vacuolar H+-PPase was dramatically decreased by pressurization from 293.9 to 70.2 micromol of PPi (pyrophosphate) consumed/h per mg of protein, while the Km value decreased from 0.35 to 0.08 mM, implying that the pressure treatment increased the affinity of PPi to vacuolar H+-PPase but decreased its hydrolysis. The physiological substrate and its analogues enhance high pressure inhibition of vacuolar H+-PPase. The HPLC profile reveals high pressure treatment of H+-PPase provokes the subunit dissociation from an active into inactive form. High hydrostatic pressure also induces the conformational change of vacuolar H+-PPase as determined by spectroscopic techniques. Our results indicate the importance of protein-protein interaction for this novel proton-translocating enzyme. Working models are proposed to interpret the pressure inactivation of vacuolar H+-PPase. We also suggest that association of identical subunits of vacuolar H+-PPase is not random but proceeds in a specific manner.

High-pressure effects on vacuolar H+-ATPase from etiolated mung bean seedlings

A high-hydrostatic-pressure technique was employed to study the structure-function relationship of plant vacuolar H+-ATPase from etiolated mung bean seedlings (Vigna radiata L.). When isolated vacuolar H+-ATPase was subjected to hydrostatic pressure, the activity of ATP hydrolysis was markedly inhibited in a time-, protein concentration- and pressure-dependent manner. The pressure treatment decreased both Vmax and Km of solubilized vacuolar H+-ATPase, implying an increase in ATP binding affinity, but a decrease in the ATP hydrolysis activity. Physiological substrate, Mg2+-ATP, augmented the loss of enzymatic activity upon pressure treatment. However, ADP, AMP, and Pi exerted substantial protective effects against pressurization. Steady-state ATP hydrolysis was more sensitive to pressurization than single-site ATPase activity. The inactivation of solubilized vacuolar H+-ATPase by pressure may result from changes in protein-protein interaction. The conformational change of solubilized vacuolar H+-ATPase induced by hydrostatic pressure was further determined by spectroscopic techniques. The inhibition of vacuolar H+-ATPase under pressurization involved at least two steps. Taken together, our work indicates that subunit-subunit interaction is crucial for the integrity and the function of plant vacuolar H+-ATPase. It is also suggested that the assembly of the vacuolar H+-ATPase complex is probably not random, but follows a sequestered pathway.

Purification and characterization of thylakoid membrane-bound inorganic pyrophosphatase from Spinacia oleracia L

An inorganic pyrophosphatase (PPase) was purified from thylakoid membrane of spinach leaves to electrophoretic purity by methods including detergent solubilization, ammonium sulfate fractionation, and successive chromatographic techniques. Current protocol yielded about 10% recovery of total activity with a 30-fold purification. The specific activity of the purified enzyme was approximately 400 micromol PPi consumed/mg protein x h. This enzyme is a monomer with a molecular mass of 55 kDa. Several properties, including subunit composition, substrate specificity, ion requirements, inhibitor sensitivities, and amino acid composition, have been studied. Mg2+ is an essential cofactor for the thylakoid PPase. The preferred substrate for the hydrolytic reaction of PPase appears to be dimagnesium pyrophosphate. K+ could not stimulate the enzymatic activity of thylakoid PPase, while F- was a potent inhibitor. Group-specific modification of the thylakoid PPase demonstrates possible involvement of carboxylate residues in the enzymatic activity. Furthermore, antibodies raised against thylakoid PPase in a rabbit could inactivate the PPi hydrolysis of thylakoid and the purified enzyme, but not that of vacuolar H+-PPase, indicating both PPi hydrolases are structurally distinct.

Subunit structure of vacuolar proton-pyrophosphatase as determined by radiation inactivation

Vacuolar proton-pyrophosphatase (H(+)-PPase) of mung bean seedlings contains a single kind of polypeptide with a molecular mass of approx. 73 kDa. However, in this study, a molecular mass of approx. 140 kDa was obtained for the purified vacuolar H(+)-PPase by size-exclusion gel-filtration chromatography, suggesting that the solubilized form of this enzyme is a dimer. Radiation inactivation analysis of tonoplast vesicles yielded functional masses of 141.5 +/- 10.8 and 158.4 +/- 19.5 kDa for PP1 hydrolysis activity and its supported proton translocation respectively. These results confirmed the in situ dimeric structure of the membrane-bound H(+)-PPase of plant vacuoles. Further target-size analysis showed that the functional unit of purified vacuolar H(+)-PPase was 71.1 +/- 6.7 kDa, indicating that only one subunit of the purified dimeric complex would sufficiently display its enzymic reaction. Moreover, in the presence of valinomycin and KCl, the functional size of membrane-bound H(+)-PPase was decreased to approx. 63.4 +/- 6.3 kDa. A working model was proposed to elucidate the structure of native H(+)-PPase on vacuolar membrane as a functional dimer. Factors that would disturb the membrane, e.g. membrane solubilization and the addition of valinomycin and KCl, may induce an alteration in its enzyme structure, subsequently resulting in a different functional size.

Involvement of tyrosine residue in the inhibition of plant vacuolar H(+)-pyrophosphatase by tetranitromethane

Plant vacuolar vesicles contain a novel H(+)-translocating pyrophosphatase (H(+)-PPase, EC 3.6.1.1). Modification of tonoplast vesicles and purified vacuolar H(+)-PPase from etiolated mung bean seedlings with tetranitromethane (TNM) resulted in a progressive decline in H(+)-translocating pyrophosphatase activity. The half-maximal inhibition was brought about by 0.6, 1.0, and 0.8 mM TNM for purified and membrane-bound H(+)-PPases, and its associated proton translocation, respectively. The maximal inhibition of vacuolar H(+)-PPase by TNM occurred at a pH value above 8. Loss of activity of purified H(+)-pyrophosphatase followed pseudo-first order rate kinetics, yielding a first-order rate constant (k2) of 0.039 s(-1) and a steady-state dissociation constant of inactivation (Ki) of 0.02 mM. Covalent modification of vacuolar H(+)-PPase by TNM increased Km value of the enzyme for its substrate without a significant effect on Vmax. Double logarithmic plots of the pseudo-first order rate constant (kobs) versus TNM concentration exhibited a slope of 0.88, suggesting that at least one tyrosine residue was involved in the inactivation of H(+)-PPase enzymatic activity. Further spectrophotometric measurements of the nitrated H(+)-pyrophosphatase indicated that TNM could modify approximately two tyrosine residues/subunit of the enzyme. However, Tsou's analysis revealed that only one of those modified tyrosine residues directly participated in the inhibition of enzymatic activity of vacuolar H(+)-PPase. The physiological substrate, i.e., dimagnesium pyrophosphate, provided substantial protection against inactivation by TNM. Moreover, NEM pretreatment of the enzyme decreased the number of subsequent nitration of vacuolar H(+)-PPase. Taken together, we suggest that vacuolar H(+)-pyrophosphatase contains a substrate-protectable tyrosine residue conferring to the inhibition of its activity and this tyrosine residue may be located in a domain sensitive to the modification of Cys-634 by NEM.

[Changes in regulatory peptides at different stages of essential hypertension and their clinical significance]

The changes of regulatory peptides in 100 patients with essential hypertension at different stages were studied. Four kinds of peptides in serum were measured by RIA method. The results showed that: (1) neurotensin, P-substances, beta-endorphin and leucine-enkephalin decreased significantly in the group (P < 0.01). (2) the levels of those parameters at different stages of hypertension were decreased in parallel with its severity and the difference between different stages is significant (P < 0.01). (3) norepinephrine showed negative correlation with four kinds of neuropeptides. (4) neurotensin, Beta-endorphin and leucine-enkephalin increased significantly after capton (P < 0.01). The possible mechanism and its clinical significance of the changes of those regulatory peptides in hypertension patients were discussed.

[Changes in the deformability of erythrocytes and 2,3-DPG in coronary artery stenosis]

The changes of deformability of RBC and 2,3-DPG in RBC in patients with coronary artery stenosis and the influence of some factors on them were studied. The results showed that: (1) the deformability index was inversely proportional to the degree of lesions of coronary vessels (P less than 0.01); (2) the 2,3-DPG was inversely proportional to the degree of lesions of coronary vessels (P less than 0.01); (3) there was a significant decrease in deformability index after using contrast medium; (4) Saliva may increase deformability of RBC and 2,3-DPG; (5) Nifedipine may increase deformability of RBC. These results showed: (1) the possible existence of microcirculatory dysfunction in coronary artery disease and in parallel of impaired deformability of RBC; (2) the possibility of normalization of the decreased deformability of 2,3-DPG in RBC by Salvia; (3) the possibility of increase of velocity of blood flow in microcirculation in coronary artery disease by Salvia.