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Katsuya Shimabukuro

Publications and source records attributed to Katsuya Shimabukuro.

8 recordsLinked to original sources
PubMed2005

Rotation scheme of V1-motor is different from that of F1-motor.

V(1), a water-soluble portion of vacuole-type ATPase (V-ATPase), is an ATP-driven rotary motor, similar to F(1)-ATPase. Hydrolysis of ATP is coupled to unidirectional rotation of the central rotor D and F subunits relative to the A(3)B(3) cylinder. In this study, we analyzed the rotation kinetics of V(1) in detail. At low ATP concentrations, the D subunit rotated stepwise, pausing every 120 degrees . The dwell time between steps revealed that V(1) consumes one ATP per 120 degrees step. V(1) generated torque of approximately 35 pN nm, slightly lower than the approximately 46 pN nm measured for F(1). Noticeably, the angles for both ATP cleavage and binding were apparently the same in V(1), in sharp contrast to F(1), which cleaves ATP at 80 degrees posterior to the binding of ATP. Thus, the mechanochemical cycle of V(1) has marked differences to that of F(1).

Adenosine Triphosphate↗
PubMed2005

An alternative reaction pathway of F1-ATPase suggested by rotation without 80 degrees/40 degrees substeps of a sluggish mutant at low ATP.

F(1)-ATPase, a water-soluble portion of F(o)F(1)-ATP synthase, is a rotary motor driven by ATP hydrolysis. The central gamma-subunit rotates in the alpha(3)beta(3) cylinder by repeating four stages of rotation: ATP-binding dwell, rapid 80 degrees substep rotation, catalytic dwell, and rapid 40 degrees substep rotation. In the catalytic dwell, at least two catalytic reactions occur-cleavage of the enzyme-bound ATP and presumably release of the hydrolyzed product(s) from the enzyme-but we found that a slow ATP cleavage mutant of F(1)-ATPase from thermophilic Bacillus PS3 rotates at low ATP concentration without substeps and the catalytic dwell. Analysis indicates that in this alternative reaction pathway the two catalytic reactions occur during the preceding long ATP-binding dwell. Thus, F(1)-ATPase can operate through (at least) two competing reaction pathways, not necessarily through a simple consecutive reaction.

Adenosine Triphosphate↗
PubMed2004

Complete inhibition and partial Re-activation of single F1-ATPase molecules by tentoxin: new properties of the re-activated enzyme.

During hydrolysis of ATP, the gamma subunit of the rotary motor protein F(1)-ATPase rotates within a ring of alpha(3)beta(3) subunits. Tentoxin is a phyto-pathogenic cyclic tetrapeptide, which influences F(1)-ATPase activity of sensitive species. At low concentrations, tentoxin inhibits ATP hydrolysis of ensembles of F(1) molecules in solution. At higher concentrations, however, ATP hydrolysis recovers. Here we have examined how tentoxin acts on individual molecules of engineered F(1)-ATPase from the thermophilic Bacillus PS3 (Groth, G., Hisabori, T., Lill, H., and Bald, D. (2002) J. Biol. Chem. 277, 20117-20119). We found that inhibition by tentoxin caused a virtually complete stop of rotation, which was partially relieved at higher tentoxin concentrations. Re-activation, however, was not simply a reversal of inhibition; while the torque appears unaffected as compared with the situation without tentoxin, F(1) under re-activating conditions was less susceptible to inhibitory ADP binding but displayed a large number of short pauses, indicating infringed energy conversion.

ATP Synthetase Complexes↗
PubMed2003

Catalysis and rotation of F1 motor: cleavage of ATP at the catalytic site occurs in 1 ms before 40 degree substep rotation.

F1, a water-soluble portion of FoF1-ATP synthase, is an ATP hydrolysis-driven rotary motor. The central gamma-subunit rotates in the alpha 3 beta 3 cylinder by repeating the following four stages of rotation: ATP-binding dwell, rapid 80 degrees substep rotation, interim dwell, and rapid 40 degrees substep rotation. At least two 1-ms catalytic events occur in the interim dwell, but it is still unclear which steps in the ATPase cycle, except for ATP binding, correspond to these events. To discover which steps, we analyzed rotations of F1 subcomplex (alpha 3 beta 3 gamma) from thermophilic Bacillus PS3 under conditions where cleavage of ATP at the catalytic site is decelerated: hydrolysis of ATP by the catalytic-site mutant F1 and hydrolysis of a slowly hydrolyzable substrate ATP gamma S (adenosine 5'-[gamma-thio]triphosphate) by wild-type F1. In both cases, interim dwells were extended as expected from bulk phase kinetics, confirming that cleavage of ATP takes place during the interim dwell. Furthermore, the results of ATP gamma S hydrolysis by the mutant F1 ensure that cleavage of ATP most likely corresponds to one of the two 1-ms events and not some other faster undetected event. Thus, cleavage of ATP on F1 occurs in 1 ms during the interim dwell, and we call this interim dwell catalytic dwell.

Adenosine Triphosphate↗
PubMed2003

Aortic arch repair for Stanford type A aortic dissection with distal anastomosis to the proximal level of the distal aortic arch.

BACKGROUND: In acute type A dissection, replacing the ascending aorta with the transverse aortic arch recently has been recommended for event-free long-term survival. Since 1994, we have performed our new transverse aortic arch replacement, in which the distal end of the graft is anastomosed between the left common carotid artery and the left subclavian artery to reduce the risk by obtaining a good surgical view, resulting in good hemostasis. The "elephant trunk technique" was used in anticipation of a staged descending aortic operation for residual dissecting aorta. We analyzed the surgical survival of patients with Stanford type A aortic dissection undergoing our operative procedure using hypothermic selective antegrade cerebral perfusion. METHODS: We performed our new technique in 27 patients (aged 61 +/- 11 years, 15 male and 12 female patients, 22 patients with acute type A dissection, and 5 patients with chronic dissection). RESULTS: One in-hospital death (3.7% in total: 4.5% in acute dissection, 0% in chronic dissection) occurred in patients undergoing our new technique. Actuarial survival (including early death) was 91% at 5 years after the operation. One late death occurred as the result of a malignant tumor. Four patients underwent a staged reoperation for aneurysmal dilatation of the residual descending aorta or renal and splenic embolism as the result of thrombus from the false lumen 2 to 11 months (mean interval 6 months) after the initial operation. They have been doing well since the reoperation. CONCLUSIONS: Our "distal anastomosis to the proximal level of the distal aortic arch" technique made aortic arch replacement easier and improved the survival of the arch replacement for aortic dissection, especially for acute type A dissection, by securing hemostasis in the suture line. Combining the elephant trunk technique with our new procedure is useful to perform a staged aortic replacement for dilatation and complication of the false lumen in the descending aorta.

Acute Disease↗
PubMed2002

The presence of phosphate at a catalytic site suppresses the formation of the MgADP-inhibited form of F(1)-ATPase.

F1-ATPase is inactivated by entrapment of MgADP in catalytic sites and reactivated by MgATP or P(i). Here, using a mutant alpha(3)beta(3)gamma complex of thermophilic F(1)-ATPase (alpha W463F/beta Y341W) and monitoring nucleotide binding by fluorescence quenching of an introduced tryptophan, we found that P(i) interfered with the binding of MgATP to F(1)-ATPase, but binding of MgADP was interfered with to a lesser extent. Hydrolysis of MgATP by F(1)-ATPase during the experiments did not obscure the interpretation because another mutant, which was able to bind nucleotide but not hydrolyse ATP (alpha W463F/beta E190Q/beta Y341W), also gave the same results. The half-maximal concentrations of P(i) that suppressed the MgADP-inhibited form and interfered with MgATP binding were both approximately 20 mm. It is likely that the presence of P(i) at a catalytic site shifts the equilibrium from the MgADP-inhibited form to the enzyme-MgADP-P(i) complex, an active intermediate in the catalytic cycle.

Adenosine Diphosphate↗