Mutagenic analysis of actin reveals the mechanism of His161 flipping that triggers ATP hydrolysis.

The dynamic assembly of actin is controlled by the hydrolysis of ATP, bound to the center of the molecule. Upon polymerization, actin undergoes a conformational change from the monomeric G-form to the fibrous F-form, which is associated with the flipping of the side chain of His161 toward ATP. His161 flipping from the gauche-minus to gauche-plus conformation leads to a rearrangement of the active site water molecules, including ATP attacking water (W1), into an orientation capable of hydrolysis. We previously showed that by using a human cardiac muscle α-actin expression system, mutations in the Pro-rich loop residues (A108G and P109A) and in a residue that was hydrogen-bonded to W1 (Q137A) affect the rate of polymerization and ATP hydrolysis. Here, we report the crystal structures of the three mutant actins bound to AMPPNP or ADP-Pi determined at a resolution of 1.35-1.55 Å, which are stabilized in the F-form conformation with the aid of the fragmin F1 domain. In A108G, His161 remained non-flipped despite the global actin conformation adopting the F-form, demonstrating that the side chain of His161 is flipped to avoid a steric clash with the methyl group of A108. Because of the non-flipped His161, W1 was located away from ATP, similar to G-actin, which was accompanied by incomplete hydrolysis. In P109A, the absence of the bulky proline ring allowed His161 to be positioned near the Pro-rich loop, with a minor influence on ATPase activity. In Q137A, two water molecules replaced the side-chain oxygen and nitrogen of Gln137 almost exactly at their positions; consequently, the active site structure, including the W1 position, is essentially conserved. This seemingly contradictory observation to the reported low ATPase activity of the Q137A filament could be attributed to a high fluctuation of the active site water. Together, our results suggest that the elaborate structural design of the active site residues ensures the precise control of the ATPase activity of actin.

Structures and mechanisms of actin ATP hydrolysis.

The major cytoskeleton protein actin undergoes cyclic transitions between the monomeric G-form and the filamentous F-form, which drive organelle transport and cell motility. This mechanical work is driven by the ATPase activity at the catalytic site in the F-form. For deeper understanding of the actin cellular functions, the reaction mechanism must be elucidated. Here, we show that a single actin molecule is trapped in the F-form by fragmin domain-1 binding and present their crystal structures in the ATP analog-, ADP-Pi-, and ADP-bound forms, at 1.15-Å resolutions. The G-to-F conformational transition shifts the side chains of Gln137 and His161, which relocate four water molecules including W1 (attacking water) and W2 (helping water) to facilitate the hydrolysis. By applying quantum mechanics/molecular mechanics calculations to the structures, we have revealed a consistent and comprehensive reaction path of ATP hydrolysis by the F-form actin. The reaction path consists of four steps: 1) W1 and W2 rotations; 2) PG-O3B bond cleavage; 3) four concomitant events: W1-PO3- formation, OH- and proton cleavage, nucleophilic attack by the OH- against PG, and the abstracted proton transfer; and 4) proton relocation that stabilizes the ADP-Pi-bound F-form actin. The mechanism explains the slow rate of ATP hydrolysis by actin and the irreversibility of the hydrolysis reaction. While the catalytic strategy of actin ATP hydrolysis is essentially the same as those of motor proteins like myosin, the process after the hydrolysis is distinct and discussed in terms of Pi release, F-form destabilization, and global conformational changes.

Structural and biochemical evidence for the emergence of a calcium-regulated actin cytoskeleton prior to eukaryogenesis.

Charting the emergence of eukaryotic traits is important for understanding the characteristics of organisms that contributed to eukaryogenesis. Asgard archaea and eukaryotes are the only organisms known to possess regulated actin cytoskeletons. Here, we determined that gelsolins (2DGels) from Lokiarchaeota (Loki) and Heimdallarchaeota (Heim) are capable of regulating eukaryotic actin dynamics in vitro and when expressed in eukaryotic cells. The actin filament severing and capping, and actin monomer sequestering, functionalities of 2DGels are strictly calcium controlled. We determined the X-ray structures of Heim and Loki 2DGels bound actin monomers. Each structure possesses common and distinct calcium-binding sites. Loki2DGel has an unusual WH2-like motif (LVDV) between its two gelsolin domains, in which the aspartic acid coordinates a calcium ion at the interface with actin. We conclude that the calcium-regulated actin cytoskeleton predates eukaryogenesis and emerged in the predecessors of the last common ancestor of Loki, Heim and Thorarchaeota.

Structural Insights into the Regulation of Actin Capping Protein by Twinfilin C-terminal Tail.

Twinfilin is a conserved actin regulator that interacts with actin capping protein (CP) via C terminus residues (TWtail) that exhibits sequence similarity with the CP interaction (CPI) motif of CARMIL. Here we report the crystal structure of TWtail in complex with CP. Our structure showed that although TWtail and CARMIL CPI bind CP to an overlapping surface via their middle regions, they exhibit different CP-binding modes at both termini. Consequently, TWtail and CARMIL CPI restrict the CP in distinct conformations of open and closed forms, respectively. Interestingly, V-1, which targets CP away from the TWtail binding site, also favors the open-form CP. Consistently, TWtail forms a stable ternary complex with CP and V-1, a striking contrast to CARMIL CPI, which rapidly dissociates V-1 from CP. Our results demonstrate that TWtail is a unique CP-binding motif that regulates CP in a manner distinct from CARMIL CPI.

Crystal structure of human V-1 in the apo form.

V-1, also known as myotrophin, is a 13 kDa ankyrin-repeat protein that binds and inhibits the heterodimeric actin capping protein (CP), which is a key regulator of cytoskeletal actin dynamics. The crystal structure of V-1 in complex with CP revealed that V-1 recognizes CP via residues spanning several ankyrin repeats. Here, the crystal structure of human V-1 is reported in the absence of the specific ligand at 2.3 Šresolution. In the asymmetric unit, the crystal contains two V-1 monomers that exhibit nearly identical structures (Cα r.m.s.d. of 0.47 Å). The overall structures of the two apo V-1 chains are also highly similar to that of CP-bound V-1 (Cα r.m.s.d.s of <0.50 Å), indicating that CP does not induce a large conformational change in V-1. Detailed structural comparisons using the computational program All Atom Motion Tree revealed that CP binding can be accomplished by minor side-chain rearrangements of several residues. These findings are consistent with the known biological role of V-1, in which it globally inhibits CP in the cytoplasm.

Novel inter-domain Ca2+-binding site in the gelsolin superfamily protein fragmin.

Gelsolin superfamily proteins, consisting of multiple domains (usually six), sever actin filaments and cap the barbed ends in a Ca2+-dependent manner. Two types of evolutionally conserved Ca2+-binding sites have been identified in this family; type-1 (between gelsolin and actin) and type-2 (within the gelsolin domain). Fragmin, a member in the slime mold Physarum polycephalum, consists of three domains (F1-F3) that are highly similar to the N-terminal half of mammalian gelsolin (G1-G3). Despite their similarities, the two proteins exhibit a significant difference in the Ca2+ dependency; F1-F3 absolutely requires Ca2+ for the filament severing whereas G1-G3 does not. In this study, we examined the strong dependency of fragmin on Ca2+ using biochemical and structural approaches. Our co-sedimentation assay demonstrated that Ca2+ significantly enhanced the binding of F2-F3 to actin. We determined the crystal structure of F2-F3 in the presence of Ca2+. F2-F3 binds a total of three calcium ions; while two are located in type-2 sites within F2 or F3, the remaining one resides between the F2 long helix and the F3 short helix. The inter-domain Ca2+-coordination appears to stabilize F2-F3 in a closely packed configuration. Notably, the F3 long helix exhibits a bent conformation which is different from the straight G3 long helix in the presence of Ca2+. Our results provide the first structural evidence for the existence of an unconventional Ca2+-binding site in the gelsolin superfamily proteins.

Structural Polymorphism of Actin.

Information on the structural polymorphism of a protein is essential to understand the mechanisms of how it functions at an atomic level. Numerous studies on actin have accumulated substantial amounts of information about its polymorphism, and there are over 200 published atomic structures of different forms of actin using crystallography, fiber diffraction, and electron microscopy. To characterize all the reported structures, we proposed simple parameters based on the discrete rigid bodies within the actin molecule and identified four conformation groups by cluster analysis: the F-form in naked F-actin, the C-form in cofilactin, the O-form in profilin-actin, and the G-form in the majority of actin-containing crystal structures. The G-form group included the most variations, but each conformational variation was convertible via a thermal fluctuation, whereas the F- and C-forms were not accessible from the G-form. The convertibility and accessibility of the structures were evaluated using molecular dynamics simulations. Information about conformational conversion among each group is useful for understanding the mechanisms of actin function.

Polymerization and depolymerization of actin with nucleotide states at filament ends.

Polymerization induces hydrolysis of ATP bound to actin, followed by γ-phosphate release, which helps advance the disassembly of actin filaments into ADP-G-actin. Mechanical understanding of this correlation between actin assembly and ATP hydrolysis has been an object of intensive studies in biochemistry and structural biology for many decades. Although actin polymerization and depolymerization occur only at either the barbed or pointed ends and the kinetic and equilibrium properties are substantially different from each other, characterizing their properties is difficult to do by bulk assays, as these assays report the average of all actin filaments in solution and are therefore not able to discern the properties of individual actin filaments. Biochemical studies of actin polymerization and hydrolysis were hampered by these inherent properties of actin filaments. Total internal reflection fluorescence (TIRF) microscopy overcame this problem by observing single actin filaments. With TIRF, we now know not only that each end has distinct properties, but also that the rate of γ-phosphate release is much faster from the terminals than from the interior of actin filaments. The rate of γ-phosphate release from actin filament ends is even more accelerated when latrunculin A is bound. These findings highlight the importance of resolving structural differences between actin molecules in the interior of the filament and those at either filament end. This review provides a history of observing actin filaments under light microscopy, an overview of dynamic properties of ATP hydrolysis at the end of actin filament, and structural views of γ-phosphate release.

Structural basis for cofilin binding and actin filament disassembly.

Actin depolymerizing factor (ADF) and cofilin accelerate actin dynamics by severing and disassembling actin filaments. Here, we present the 3.8 Å resolution cryo-EM structure of cofilactin (cofilin-decorated actin filament). The actin subunit structure of cofilactin (C-form) is distinct from those of F-actin (F-form) and monomeric actin (G-form). During the transition between these three conformations, the inner domain of actin (subdomains 3 and 4) and the majority of subdomain 1 move as two separate rigid bodies. The cofilin-actin interface consists of three distinct parts. Based on the rigid body movements of actin and the three cofilin-actin interfaces, we propose models for the cooperative binding of cofilin to actin, preferential binding of cofilin to ADP-bound actin filaments and cofilin-mediated severing of actin filaments.

Comprehensive analysis of motions in molecular dynamics trajectories of the actin capping protein and its inhibitor complexes.

The actin capping protein (CP) binds to actin filaments to block further elongation. The capping activity is inhibited by proteins V-1 and CARMIL interacting with CP via steric and allosteric mechanisms, respectively. The crystal structures of free CP, CP/V-1, and CP/CARMIL complexes suggest that the binding of CARMIL alters the flexibility of CP rather than the overall structure of CP, and this is an allosteric inhibition mechanism. Here, we performed molecular dynamics (MD) simulations of CP in the free form, and in complex with CARMIL or V-1. The resulting trajectories were analyzed exhaustively using Motion Tree, which identifies various rigid-body motions ranging from small local motions to large domain motions. After enumerating all the motions, CP flexibilities with different ligands were characterized by a list of frequencies for 20 dominant rigid-body motions, some of which were not identified in previous studies. The comparative analysis highlights the influence of the binding of the CARMIL peptide to CP flexibility. In free CP and the CP/V-1 complex, domain motions around a large crevice between the N-stalk and the CP-S domain occur frequently. The CARMIL peptide binds the crevice and suppresses the motions effectively. In addition, the binding of the CARMIL peptide enhances and alters local motions around the pocket that participates in V-1 binding. These newly identified motions are likely to suppress the binding of V-1 to CP. The observed changes in CP motion provide insights that describe the mechanism of allosteric regulation by CARMIL through modulating CP flexibility. Proteins 2016; 84:948-956. © 2016 Wiley Periodicals, Inc.

Effects of lipid composition and solution conditions on the mechanical properties of membrane vesicles.

The mechanical properties of cell-sized giant unilamellar liposomes were studied by manipulating polystyrene beads encapsulated within the liposomes using double-beam laser tweezers. Mechanical forces were applied to the liposomes from within by moving the beads away from each other, which caused the liposomes to elongate. Subsequently, a tubular membrane projection was generated in the tip at either end of the liposome, or the bead moved out from the laser trap. The force required for liposome transformation reached maximum strength just before formation of the projection or the moving out of the bead. By employing this manipulation system, we investigated the effects of membrane lipid compositions and environment solutions on the mechanical properties. With increasing content of acidic phospholipids, such as phosphatidylglycerol or phosphatidic acid, a larger strength of force was required for the liposome transformation. Liposomes prepared with a synthetic dimyristoylphosphatidylcholine, which has uniform hydrocarbon chains, were transformed easily compared with liposomes prepared using natural phosphatidylcholine. Surprisingly, bovine serum albumin or fetuin (soluble proteins that do not bind to membranes) decreased liposomal membrane rigidity, whereas the same concentration of sucrose showed no particular effect. These results show that the mechanical properties of liposomes depend on their lipid composition and environment.

Actin capping protein and its inhibitor CARMIL: how intrinsically disordered regions function.

The actin capping protein (CP) tightly binds to the barbed end of actin filaments to block further elongation. The ß-tentacle in CP is an important region that ensures stable interaction with actin filaments. CARMIL inhibits the interaction of CP with actin filaments via the C-terminal portion containing the CP-binding motif, located in an intrinsically disordered region. We have proposed an allosteric inhibition model in which CARMIL suppresses CP by the population shift mechanism. Here, we solved a crystal structure of CP in complex with a CARMIL-derived peptide, CA32. The new structure clearly represents the α-helical form of the ß-tentacle that was invisible in other CP/CARMIL peptide complex structures. In addition, we exhaustively performed a normal mode analysis with the elastic network model on all available crystal structures of the CP/CARMIL peptide complexes, including the new structure. We concluded that the CP-binding motif is necessary and sufficient for altering the fluctuation of CP, which is essential for attenuating the barbed-end-capping activity along the population shift mechanism. The roles and functions of the ß-tentacle and the CP-binding motif are discussed in terms of their intrinsically disordered nature.

Electron microscopic visualization of the filament binding mode of actin-binding proteins.

A large number of actin-binding proteins (ABPs) regulate various kinds of cellular events in which the superstructure of the actin cytoskeleton is dynamically changed. Thus, to understand the actin dynamics in the cell, the mechanisms of actin regulation by ABPs must be elucidated. Moreover, it is particularly important to identify the side, barbed-end or pointed-end ABP binding sites on the actin filament. However, a simple, reliable method to determine the ABP binding sites on the actin filament is missing. Here, a novel electron microscopic method for determining the ABP binding sites is presented. This approach uses a gold nanoparticle that recognizes a histidine tag on an ABP and an image analysis procedure that can determine the polarity of the actin filament. This method will facilitate future study of ABPs.

Effects of TJN-598, a new selective phosphodiesterase type IV inhibitor on anti-Thy1 nephritis in rats.

BACKGROUND: Phosphodiesterase type IV (PDEIV) plays an important role in the immune response and inflammation. However, it is well known that classical PDEIV inhibitors have systemic side effects, so the clinical and chronic use of these agents as therapy for glomerulonephritis is difficult. This study was performed to elucidate the anti-nephritic effects of TJN-598, a new chemical compound derived from herbal components, on experimental mesangial proliferative glomerulonephritis. METHODS: We first examined the effects of TJN-598 and captopril on mesangial expansion induced by anti-Thy1 serum in rats. Second, to investigate the effects of TJN-598 and rolipram, which are typical PDEIV inhibitors, on the production of tumor necrosis factor (TNF)-α and transforming growth factor (TGF)-ß1, glomeruli were isolated from rats with anti-Thy1 nephritis and incubated with the test drugs in vitro for 48 h. RESULTS: Treatment with TJN-598 prevented an increase in the mesangial area/total glomerular area, in the number of cells in the glomerular cross section and matrix index. TJN-598 also inhibited the increases in the expression of α-smooth muscle actin, the TGF-ß1-positive area, in the number of ED-1 positive cells and proliferating cell nuclear antigen-positive cells in the glomeruli. Furthermore, administration of TJN-598 inhibited increases in the levels of TGF-ß1 protein derived from glomeruli with anti-Thy-1 nephritis. The addition of both TJN-598 and rolipram to the culture supernatant inhibited both increased expression of TGF-ß1 and increases in levels of TNF-α in glomeruli isolated from rats with anti-Thy1 nephritis in a dose-dependent manner. CONCLUSION: These results suggest that TJN-598, a PDEIV inhibitor, is effective against expansion of mesangial cells, via the suppression of secretion of TGF-ß1 and TNF-α from inflamed glomeruli.

Clustering analysis of keishibukuryogan formulas by use of self-organizing maps.

Kampo medicines, traditional herbal medicines in Japan, are comprised of multiple botanical raw materials that contain a number of pharmacologically active substances. Conventionally, the quality control of kampo medicines has been performed by analyzing the contents of two or three representative components. However, it is not sufficient to check quality only with a limited number of specific components. We performed HPLC of 287 lots of keishibukuryogan formulas, calculated the areas of 11 components on chromatograms as feature values and made a cluster analysis using self-organizing maps (SOMs). We verified the precision (repeatability and intermediate precision) of clustering results when using the same samples and successfully established an clustering method using SOMs that is capable of precisely clustering differences in HPLC-fingerprints among pharmaceutical manufacturers, differences in HPLC-fingerprints due to the combination ratios of botanical raw materials, and differences in HPLC-fingerprints due to changes in component contents caused by time-course deterioration. Consequently, we could confirm that this method is useful for controlling the quality of multiple component drugs and analyzing quality differences.

Effect of TJN-331 on anti-Thy1 nephritis in rats via inhibition of transforming growth factor-ß1 production.

This study was performed to examine the effects of the antifibrotic agents TJN-331 and tranilast on mesangial expansion in a rat model of anti-Thy1 nephritis. We first investigated the effects of TJN-331 and tranilast on mesangial expansion induced by anti-Thy1 serum in rats, and determined the counts of glomerular cells and proliferative cell nuclear antigen (PCNA)-positive cells. The effects of TJN-331 and tranilast on production of transforming growth factor-ß1 (TGF-ß1) by isolated glomeruli incubated for 48 h were then examined. The TGF-ß1 staining score, the number of TGF-ß1-positive cells and the TGF-ß1 receptor-positive area in the anti-Thy1 nephritis model were also measured using immunohistochemistry. TJN-331 administered from day 1 (the day after anti-Thy1 serum injection) blocked an increase in mesangial matrix accumulation on days 4 and 8, compared to untreated anti-Thy1 nephritic rats. TJN-331 also inhibited both the increase in the number of glomerular cells on day 8 and the decrease in this cell count on day 2 observed in untreated nephritic rats, and TJN-331 and tranilast inhibited an increase in PCNA-positive cells in the glomerular cross section on days 4 and 8. Both TJN-331 and tranilast inhibited increases in the TGF-ß1 protein content from nephritic glomeruli, the TGF-ß1-positive area, and the number of TGF-ß1-positive cells/cross section in anti-Thy1 nephritic glomeruli. These results suggest that TJN-331 and tranilast prevent expansion of the mesangial area by suppression of TGF-ß1 secretion from inflamed glomeruli.

(E)-N-[(3,4-dimethoxyphenethyl)]-N-methyl-3-(3-pyridyl)-2-propenamide (TJN-331) inhibits mesangial expansion in experimental IgA nephropathy in ddY mice.

BACKGROUND: TJN-331 is an inhibitor of transforming growth factor ß1 (TGF-ß1) production that has similar structural features to the natural product acteoside. This study was performed to examine the antinephritic effects of TJN-331 in a mouse model of experimental IgA nephropathy. MATERIALS AND METHODS: IgA nephropathy was induced in ddY mice by oral administration of bovine γ globulin, followed by reticuloendothelial blocking by colloidal carbon injection and heminephrectomy. Effects of TJN-331 were examined over oral administration periods from 10 to 15 weeks after the third colloidal carbon injection. Intravenous administration of a TGF-ß1-neutralizing antibody was used to investigate the role of TGF-ß1 in IgA nephropathy. RESULTS: Administration of TJN-331 or captopril prevented elevation of serum creatinine. Histopathological examination after both experimental periods showed that TJN-331 inhibited increases in the mesangial matrix index and the number of nuclei per glomerular cross-section, compared with in untreated ddY mice with IgA nephropathy. TJN-331 prevented increase in glomerular TGF-ß1 staining without affecting IgA. In the in vitro study, TJN-331 prevented total TGF-ß1 production from splenocytes stimulated with concanavalin A. A neutralizing antibody against TGF-ß1 prevented increase in the mesangial matrix index and the number of glomerular cells per cross-sectional area. CONCLUSION: These results suggest that TJN-331 is effective against IgA nephropathy in ddY mice and acts via suppression of TGF-ß1 production in glomeruli.

TJN-331 improves anti-glomerular basement membrane nephritis by inhibiting the production of intraglomerular transforming growth factor-beta1.

Transforming growth factor-beta1 (TGF-beta1) plays an important role in the development of glomerulonephritis. The study of experimental glomerulonephritis in rats was performed to examine the antinephritic effects of TJN-331, a new herbally-derived chemical compound. To clarify the action of TJN-331 ((E)-N-(3,4-dimethoxyphenethyl)-N-methyl-3-(3-pyridyl)-2-propenamide) on TGF-beta1 production, glomeruli were isolated from rats with antiglomerular basement membrane (GBM) nephritis and incubated for 48 h with test drugs in vitro. Next, we examined the effects of TJN-331 on rat anti-GBM nephritis induced by injection with anti-GBM serum. TJN-331 dose-dependently inhibited the increase in total and mature TGF-beta1 production from nephritic glomeruli, although it did not inhibit TGF-beta1 production from normal glomeruli. Administration of TJN-331, at a dose of 2 mg/kg/d, per os (p.o.), prevented proteinuria and increased crescent formation and adhesion of capillary walls to Bowman's capsule. The increases in mature TGF-beta1 protein production and TGF-beta1 staining score in nephritic rats were reversed by TJN-331 treatment. These results suggest that TJN-331 inhibits proteinuria and histopathological changes in glomeruli via suppression of TGF-beta1 production from inflamed glomeruli.

Two distinct mechanisms for actin capping protein regulation--steric and allosteric inhibition.

The actin capping protein (CP) tightly binds to the barbed end of actin filaments, thus playing a key role in actin-based lamellipodial dynamics. V-1 and CARMIL proteins directly bind to CP and inhibit the filament capping activity of CP. V-1 completely inhibits CP from interacting with the barbed end, whereas CARMIL proteins act on the barbed end-bound CP and facilitate its dissociation from the filament (called uncapping activity). Previous studies have revealed the striking functional differences between the two regulators. However, the molecular mechanisms describing how these proteins inhibit CP remains poorly understood. Here we present the crystal structures of CP complexed with V-1 and with peptides derived from the CP-binding motif of CARMIL proteins (CARMIL, CD2AP, and CKIP-1). V-1 directly interacts with the primary actin binding surface of CP, the C-terminal region of the alpha-subunit. Unexpectedly, the structures clearly revealed the conformational flexibility of CP, which can be attributed to a twisting movement between the two domains. CARMIL peptides in an extended conformation interact simultaneously with the two CP domains. In contrast to V-1, the peptides do not directly compete with the barbed end for the binding surface on CP. Biochemical assays revealed that the peptides suppress the interaction between CP and V-1, despite the two inhibitors not competing for the same binding site on CP. Furthermore, a computational analysis using the elastic network model indicates that the interaction of the peptides alters the intrinsic fluctuations of CP. Our results demonstrate that V-1 completely sequesters CP from the barbed end by simple steric hindrance. By contrast, CARMIL proteins allosterically inhibit CP, which appears to be a prerequisite for the uncapping activity. Our data suggest that CARMIL proteins down-regulate CP by affecting its conformational dynamics. This conceptually new mechanism of CP inhibition provides a structural basis for the regulation of the barbed end elongation in cells.

Pharmacokinetics of [6]-shogaol, a pungent ingredient of Zingiber officinale Roscoe (Part I).

To investigate the pharmacokinetics of [6]-shogaol, a pungent ingredient of Zingiber officinale Roscoe, the pharmacokinetic parameters were determined by using (14)C-[6]-shogaol (labeled compound) and [6]-shogaol (non-labeled compound). When the labeled compound was orally administered to rats, the maximum plasma concentration (C (max)) and the area under the curve (AUC) of plasma radioactivity concentration increased in a dose-dependent manner. When the labeled compound was orally administered at a dose of 10 mg/kg, 20.0 + or - 1.8% of the radioactivity administered was excreted into urine, 64.0 + or - 12.9% into feces, and 0.2 + or - 0.1% into breath. Thus, more of the radioactivity was excreted into feces than into urine, and almost no radioactivity was excreted into breath. Furthermore, when the labeled compound was orally administered at a dose of 10 mg/kg, cumulative biliary radioactivity excretion over 48 h was 78.5 + or - 4.5% of the radioactivity administered, and cumulative urinary radioactivity excretion over 48 h was 11.8 + or - 2.7%, showing that about 90% of the dose administered orally was absorbed from the digestive tract and most of the fecal excretion was via biliary excretion. On the other hand, when the non-labeled compound [6]-shogaol was orally administered, the plasma concentration and biliary excretion of the unchanged form were extremely low. When these results are combined with those obtained with the labeled compound, it would suggest that [6]-shogaol is mostly metabolized in the body and excreted as metabolites.