The outer membrane protein OprM of Pseudomonas aeruginosa is encoded by oprK of the mexA-mexB-oprK multidrug resistance operon

An outer membrane protein (OprK) overproduced in a multiply antibiotic-resistant strain of Pseudomonas aeruginosa was previously identified as the product of the third gene of a multidrug resistance operon, mexA-mexB-oprK (K. Poole, K. Krebes, C. McNally, and S. Neshat, J. Bacteriol. 175:7363-7372, 1993). To determine whether this protein was identical to another outer membrane protein (OprM) also overproduced in some multiply resistant strains, attempts were made to map the transposon insertion site of several OprM-deficient mutants to the mex operon. Amplification of chromosomal DNA of several Tn5 insertion OprM-deficient mutants with primers specific to each gene of the mex operon revealed that the transposon had inserted into mexB in one instance and into oprK in two others. Furthermore, introduction of the cloned mexA-mexB-oprK operon into these mutants restored expression of multidrug resistance, concomitant with OprM production. These data demonstrated that OprM is encoded by the mex operon. OprM and OprK were not, however, immunologically cross-reactive, indicating that they are distinct proteins and that OprK is, in fact, not encoded by the mex operon. This operon is thus renamed mexA-mexB-oprM.

Localization of macrophage migration inhibitory factor (MIF) to secretory granules within the corticotrophic and thyrotrophic cells of the pituitary gland

BACKGROUND

Macrophage migration inhibitory factor (MIF) was one of the first lymphokine activities to be discovered and was described almost 30 years ago to be a soluble factor(s) produced by activated T lymphocytes. In more recent studies, MIF has been "rediscovered" to be an abundant, pre-formed constituent of the anterior pituitary gland and the macrophage, and to be a critical component in the host response to septic shock. Pituitary-derived MIF enters the circulation after infectious or stressful stimuli and appears to act to counterregulate glucocorticoid suppression of cytokine production.

MATERIALS AND METHODS

Immunoelectron microscopy utilizing a combination of anti-MIF and anti-pituitary hormone-specific antibodies was used to study the ultrastructural localization of MIF within the anterior pituitary gland. Pituitaries were obtained from resting, unstimulated mice and from mice 16 hr after endotoxin administration. The release of MIF also was investigated in vitro by examining the effect of corticotropin-releasing hormone (CRH_ on the AtT-20, corticotrophic cell line.

RESULTS

MIF localizes to granules present exclusively in ACTH and TSH secreting cells. Within each cell type, a subset of granules was found to contain both MIF and ACTH, or MIF and TSH. The pituitary content of MIF-containing granules decreased significantly after experimentally induced endotoxemia. In seven pituitaries examined 16 hr after LPS injection, the number of MIF-positive granules diminished by 38% in corticotrophic cells and by 48% in thyrotrophic cells when compared with controls (p < 0.05). CRH was observed to be a potent MIF secretagogue in vitro, inducing the release of MIF from corticotrophic cells at concentrations lower than that required for ACTH release.

CONCLUSION

These data provide ultrastructural information that identify MIF to be a novel anterior pituitary hormone, support earlier studies showing a time-dependent release of pituitary MIF during endotoxemia, and suggest an important, systemic role for MIF in the stress response to infection and other stimuli.

Antibacterial properties of AM-1155, a new 8-methoxy quinolone

AM-1155 is a new 8-methoxy quinolonecarboxylic acid with a broad spectrum of antibacterial activity. It inhibited more than 90% of clinical isolates of methicillin-susceptible Staphylococcus aureus, streptococci, Enterococcus faecalis, most of the Enterobacteriaceae, Acinetobacter calcoaceticus and Haemophilus influenzae at the concentration of 0.39 mg/L. AM-1155 was 2- to 16-fold more active than ciprofloxacin against Gram-positive organisms including methicillin-resistant staphylococci. The antibacterial activity of AM-1155 was almost equal to that of sparfloxacin against a wide range of Gram-positive and Gram-negative species. AM-1155 also showed a good activity against anaerobes. The protective efficacy of AM-1155 against experimental systemic infections with Gram-positive and Gram-negative pathogens in mice was almost equal or superior to that of sparfloxacin. AM-1155 was 5- to 28-times more effective than ciprofloxacin, in terms of ED50 at one week, in staphylococcal and streptococcal infections.

Upper airway obstruction during midazolam sedation: modification by nasal CPAP

We examined the depressant effect of midazolam on respiration in 21 healthy women undergoing lower abdominal surgery with spinal anaesthesia. Airway gas flow, airway pressure, and the sound of snoring were recorded together with arterial oxygen saturation (SpO2). After spinal anaesthesia was established, subjects were deeply sedated with pentazocine 15 mg followed by incremental doses of midazolam 1 mg i.v. up to 0.1 mg.kg-1. When SpO2 decreased to < 90% or snoring and/or apnoea was observed, continuous positive airway pressure applied through the nose (nasal CPAP) was increased until the respiratory deterioration was reversed. While one patient remained free of respiratory events, the other 20 patients were successfully treated with nasal CPAP restoring normal SpO2 (95.5 +/- 1.7%) without snoring. Stepwise reduction of nasal CPAP determined the minimally effective CPAP to prevent snoring to be 5.1 +/- 2.1 cm H2O. Further reduction of nasal CPAP induced snoring in 15 patients and obstructive apnoea in five patients with the latter accompanied by a severe reduction of SpO2 (87.4 +/- 6.1%). Patients with apnoea were older than those who snored (P < 0.05. We conclude that upper airway obstruction contributes considerably to decreases in SpO2 during midazolam sedation for spinal anaesthesia.

Flavoprotein structure and mechanism. 4. Xanthine oxidase and xanthine dehydrogenase

Xanthine oxidase and xanthine dehydrogenase are enzymes involved in the metabolism of purines and pyrimidines in various organisms. Their relationship to one another has been the subject of considerable debate, primarily because of their proposed roles in ischemia/reperfusion damage in tissues. Differences in the kinetics and oxidation-reduction behavior of the two forms are accounted for by the presence in the dehydrogenase of a binding site for NAD+, as well as a substantially lower reduction potential for the flavin FADH./FADH2 couple of the dehydrogenase relative to the oxidase. This review presents recent advances of our understanding of the biochemistry and molecular biology of these systems, including a model for the overall morphology of xanthine oxidizing enzymes. The evidence that the two enzymes represent alternate forms of the same gene product, in some cases reversibly interconvertible between one another, is discussed.

Purification of a 54-kilodalton protein (OprJ) produced in NfxB mutants of Pseudomonas aeruginosa and production of a monoclonal antibody specific to OprJ

The 54-kDa outer membrane protein (designated OprJ) of a norfloxacin-resistant nfxB mutant of Pseudomonas aeruginosa PAO1 was purified by ion-exchange high-performance liquid chromatography. Mobility of OprJ in sodium dodecyl sulfate-polyacrylamide gel electrophoresis was not affected by reduction and heating. A murine monoclonal antibody (MAb) against OprJ was prepared to investigate existence of this protein in fluoroquinolone-susceptible and -resistant strains of P. aeruginosa. Western blot (immunoblot) analysis with this MAb revealed a single band at the position corresponding to OprJ in outer membrane proteins of NfxB mutants derived from clinical isolates. However, the MAb did not react with any outer membrane proteins of the respective parent strains. Complementation of the NfxB mutation by transformation with plasmid pNF111, which contained the wild-type nfxB gene, led to disappearance of the single band corresponding to OprJ. The existence of OprJ was associated with fluoroquinolone resistance. Furthermore, the MAb did not react with any outer membrane proteins of other fluoroquinolone-resistant nalB and nfxC mutants. These results suggest that OprJ is newly produced in NfxB mutants of P. aeruginosa and is involved in fluoroquinolone resistance specific to NfxB, and it appears that the MAb to OprJ should aid in detection of the NfxB mutation in P. aeruginosa.

Significance of Phe-220 and Gln-221 in the catalytic mechanism of farnesyl diphosphate synthase of Bacillus stearothermophilus

Farnesyl diphosphate synthase [EC 2.5.1.10] from Bacillus stearothermophilus was specifically altered at two amino acid residues by using site-directed mutagenesis. The highly conserved Phe and Gln residues at the sequential amino acid positions 220-221 in an upstream part of the putative substrate binding site were replaced with Ala and Glu, respectively. These mutageneses (F220A and Q221E) resulted in 10(-5) and 10(-3) decreases in catalytic activity of farnesyl diphosphate synthesis, respectively. Michaelis constants of the Q221E mutant for the allylic substrates (dimethylallyl- and geranyl diphosphates) increased approximately 25- and 2-folds, respectively, compared to wild type, whereas those for the homoallylic substrate (isopentenyl diphosphate) were not altered much. These results suggest that the Phe-Gln motif is involved not only in the binding of allylic substrates but also in the catalysis by farnesyl diphosphate synthase.

Cytosolic mercaptopyruvate sulfurtransferase is evolutionarily related to mitochondrial rhodanese. Striking similarity in active site amino acid sequence and the increase in the mercaptopyruvate sulfurtransferase activity of rhodanese by site-directed mutagenesis

Rat liver mercaptopyruvate sulfurtransferase (MST) was purified to homogeneity. MST is very similar to rhodanese in physicochemical properties. Further, rhodanese cross-reacts with anti-MST antibody. Both purified authentic MST and expressed rhodanese possess MST and rhodanese activities, although the ratio of rhodanese to MST activity is low in MST and high in rhodanese. In order to compare the active site regions of MST and rhodanese, the primary structure of a possible active site region of MST was determined. The sequence showed 66% homology with that of rat liver rhodanese. An active site cysteine residue (Cys246; site of formation of persulfide in catalysis) and an arginine residue (Arg185; substrate binding site) in rhodanese were also conserved in MST. On the other hand, two other active site residues (Arg247 and Lys248) were replaced by Gly and Ser, respectively. Conversion of rhodanese to MST was tried by site-directed mutagenesis. After cloning of rat liver rhodanese, recombinant wild type and three mutants (Arg247-->Gly and/or Lys248-->Ser) were constructed. The enzymes were expressed in Escherichia coli strain BL21 (DE3) with a T7 promoter system. The mutation of these residues decreases rhodanese activity and increases MST activity.

Improved bactericidal activity of Q-35 against quinolone-resistant staphylococci

The bactericidal effects of Q-35, sparfloxacin, tosufloxacin, and ofloxacin on 18 strains of methicillin-resistant Staphylococcus aureus (MRSA) and 3 strains of Staphylococcus epidermidis were studied by a viable-count method. Staphylococci as used in this study were clearly divided into two groups with respect to their susceptibilities to sparfloxacin. MICs of Q-35 and tosufloxacin were 0.05 to 0.78 microgram/ml for sparfloxacin-susceptible strains (MICs, 0.05 to 0.2 microgram/ml) and 1.56 to 12.5 micrograms/ml for sparfloxacin-resistant strains (6.25 to 25 micrograms/ml). All the sparfloxacin-resistant strains of MRSA tested contained the gyrA mutation at codon 84. Time-kill studies showed that Q-35 decreased the viable counts from approximately 10(7) CFU/ml to 10(3) to 10(5) CFU/ml within 3 h at concentrations greater than the MICs against both sparfloxacin-susceptible and -resistant strains. In contrast, sparfloxacin, tosufloxacin, and ofloxacin produced bacteriostatic effects at 3 h after exposure against sparfloxacin-resistant strains at concentrations which were greater than the respective MICs, whereas these quinolones were bactericidal against sparfloxacin-susceptible strains. The rapid bactericidal activities of Q-35 against sparfloxacin-resistant MRSA were reduced when the methoxy group of Q-35 at the 8 position was substituted with fluorine or hydrogen. Thus, our data suggest that the introduction of a methoxy group into the 8 position of quinolones contributes to the bactericidal activities of fluoroquinolones against quinolone-resistant staphylococci.

Hepatocyte growth factor as a hematopoietic regulator

Hepatocyte growth factor (HGF) was originally isolated as a mitogen for adult hepatocytes, but this cytokine is now regarded as a multi-functional factor. In the present study, we show that the mouse liver in the middle and/or late stage of the fetal life expresses both HGF and c-met (its receptor) messages. HGF and c-met mRNA are coexpressed not only in the adherent layers of fetal liver long-term cultures (FL-LTCs) and adult bone marrow long-term cultures (BM-LTCs), but also in the stromal cell lines MS-5 and PA-6. Addition of human HGF (2 and 20 ng/mL) to the LTCs enhances (1) nonadherent cell counts (ninefold in FL-LTCs and sixfold in BM-LTCs), (2) nonadherent colony-forming unit-in culture (CFU-C) counts (eightfold in FL-LTCs and fivefold in BM-LTC), and (3) cobblestone colony counts. However, HGF slightly inhibits the proliferation of stromal cells. No direct effect of HGF on freshly isolated BM and/or FL cells is found in the CFU-C assay. However, an approximately 1.5-fold synergistic increase in CFU-C counts is noted when the BM or FL cells are cocultured with HGF in the presence of interleukin-3. These findings strongly suggest that HGF plays a crucial role as a hematopoietic regulator in the proliferation and differentiation of hematopoietic progenitors.

Ventilatory responses to inspiratory resistive loading before and after gastrectomy during isoflurane anesthesia

We tested the hypothesis that steady-state responses to inspiratory-flow-resistive loading would be preserved immediately after upper abdominal surgery in anesthetized patients. Twenty patients were studied immediately before and after gastrectomy under 1 minimum alveolar anesthetic concentration (MAC) of isoflurane anesthesia. Ventilation, airway occlusion pressure, and Paco2 were measured before and during inspiratory-flow-resistive breathing lasting from 6 to 7 min. Ten of 20 subjects were tested with resistance of 51.8 cm H2O.L-1.s-1 (Load 1) and the remaining 10 subjects were tested with resistance of 83.3 cm H2O.L-1.s-1 (Load 2). Ventilatory variables obtained immediately before and after surgery were compared in each group. Baseline ventilation increased postoperatively with greater frequency of breathing and comparable tidal volume (VT). Immediately after the application of resistive load, minute ventilation (VI) significantly decreased both pre- and postoperatively, due primarily to the decrease of VT. During sustained loading, VI gradually increased and reached steady state in 2-3 min. After 5 min of loading, Paco2 returned to the control level with Load 1 whereas with Load 2, it was higher than the control value. The magnitude and time course of reduced ventilation in response to resistive load were identical between pre- and postoperative conditions. We conclude that the ability of maintaining ventilation to imposed inspiratory-flow-resistive loading is well preserved during 1 MAC of isoflurane anesthesia before and after gastrectomy.

[Synergism of ciprofloxacin and roxithromycin to Pseudomonas aeruginosa biofilm]

Synergism of ciprofloxacin (CPFX) and roxithromycin (RXM) to bacterial biofilms formed by Pseudomonas aeruginosa was investigated. Measurement of antibacterial activities and morphological observation with a scanning electron-microscope suggested that RXM eradicated the biofilms by unknown mechanism and thereby enhanced the bactericidal activity of CPFX to P. aeruginosa in biofilms.

Mechanism of inhibition of xanthine oxidase with a new tight binding inhibitor

The mechanism of inhibition of milk xanthine oxidase and xanthine dehydrogenase by the tight binding inhibitor, sodium-8-(3-methoxy-4-phenylsulfinylphenyl)pyrazolo[1,5-a]-1,3,5- triazine-4-olate monohydrate (BOF-4272), was studied after separation of the two isomers. The steady state kinetics showed that the inhibition by these compounds was a mixed type. One of the isomers had a Ki value of 1.2 x 10(-9) M and a Ki' value of 9 x 10(-9) M, while the other isomer had a Ki value of 3 x 10(-7) M and a Ki' value of 9 x 10(-6) M. Spectral changes were not observed by mixing either the oxidized or reduced form of the enzyme with BOF-4272. The stopped-flow study and the effects of BOF-4272 on various substrates showed that BOF-4272 bound to the xanthine binding site of the enzyme. Kd values of the enzyme and one of the isomers, which has a higher affinity for the enzyme, were also found to be 2 x 10(-9) M for the active form of the enzyme and 7 x 10(-9) M for the desulfo-form using fluorometric titration, and the binding has stoichiometry of 1:1. The inhibitor could not bind to the enzyme when the enzyme was previously treated with oxipurinol.

Antibiotic susceptibility of the sputum pathogens and throat swab pathogens isolated from the patients undergoing treatment in twenty-one private clinics in Japan

Bacteriology of the respiratory isolates from 2,539 patients with respiratory infections in 21 primary care clinics was documented. Of a total of 1,887 strains of potential pathogens recovered from 1,507 patients, 996 were gram-positive and 891 were gram-negative. Major pathogens were Staphylococcus aureus, Haemophilus influenzae, Streptococcus pneumoniae and Streptococcus pyogenes. The MIC's against microbial isolates of six antimicrobial agents were determined. Ciprofloxacin and ofloxacin were more active against S. aureus, Moraxella catarrhalis and Pseudomonas aeruginosa, and ampicillin and cefteram were more active against S. pnuemoniae and S. pyogenes than four other antimicrobials tested, respectively, in this experiment. New quinolones and new generation cephems were active against H. influenzae and Enterobacteriaceae. Only one strain of S. aureus was methicillin-resistant. As regards other pathogens, 6.5% of S. pneumoniae and 14.9% of H. influenzae were resistant to ampicillin, and 26.7% of H. influenzae were beta-lactamase-positive. MRSA was found infrequently. But ampicillin-resistant S. pneumoniae and H. influenzae were found in primary care clinics almost as frequently as in intensive-medication-oriented clinics.

Successful bone marrow transplantation by bone grafts in chimeric-resistant combination

It has been shown that the bone marrow cells (BMCs) of DBA/2 mice do not readily take in bone marrow from C57BL/6 mice, even if more than 5 x 10(6) cells are injected. In this paper, we show that such chimerism resistance can be overcome by cografting DBA/2 bones from which the hematopoietic cells have been removed but in which the stromal cells remain. C57BL/6 mice reconstituted with BMCs plus bones of DBA/2 mice survive significantly longer than C57BL/6 mice reconstituted with DBA/2 BMC alone. In the former, not only the hematolymphoid cells but also the stromal cells are replaced by donor-type cells, whereas in the latter, the donor hematolymphoid cells are rejected. These findings indicate that the stromal cells in the engrafted bones play a crucial role in the prevention of graft rejection in bone marrow transplantation.

Role of cysteine 337 and cysteine 340 in flavoprotein that functions as NADH oxidase from Amphibacillus xylanus studied by site-directed mutagenesis

A flavoprotein from Amphibacillus xylanus catalyzes the reduction of oxygen to hydrogen peroxide. Each polypeptide chain in the tetrameric enzyme contains 5 cysteine residues. The complete reduction of enzyme by dithionite requires 6 electrons. Such behavior indicates the presence of redox centers in addition to the FAD, and these could be disulfides. In order to assess the catalytic role of disulfide in the enzyme, 2 of the cysteines (Cys-337 and Cys-340), which show a high degree of homology with alkyl hydroperoxide reductase F52a protein and thioredoxin reductase, have been changed to serines by site-directed mutagenesis of the cloned flavoprotein gene (individually and in a double mutant). Titration of the three mutant enzymes, lacking Cys-337, Cys-340, or both cysteines, requires only 2 electron eq to reach the reduced flavin state. These results indicate the absence of a redox-active disulfide and demonstrate the involvement of Cys-337 and Cys-340 in the redox-active disulfide. The catalytic activity of the three enzymes was examined by steady-state analysis. The Km for NADH and oxygen and the kcat value of these mutant enzymes were essentially the same as those of wild type. The NADH oxidase activities were also accelerated markedly in the presence of free FAD, which is the case for wild-type enzyme. The NADH:5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) oxidoreductase activities of all mutant enzymes were less than 3% of the activity of wild-type enzyme. The weak DTNB reductase activities in the mutant enzymes lacking Cys-337 or Cys-340 may occur through direct reduction of the mixed disulfide Cys-337-thiol or Cys-340-thiol and nitrothiobenzoate by FADH2. However, the weak DTNB reductase activity in the mutant enzyme lacking both cysteines indicates that FADH2 can reduce either DTNB or another disulfide directly, albeit inefficiently. These results suggest intramolecular dithiol-disulfide interchange reactions in the flavoprotein.

Cloning, expression, and characterization of cDNAs encoding Arabidopsis thaliana squalene synthase

We have isolated and characterized two overlapping cDNA clones for Arabidopsis thaliana squalene synthase. Their nucleotide sequences contained an open reading frame for a 410-amino acid polypeptide (calculated molecular mass, 47 kDa). The deduced amino acid sequence of the Arabidopsis polypeptide was significantly homologous (42-44% identical) to the sequences of known squalene synthases of several species, from yeast to man, but it was much less homologous to that of tomato phytoene synthase. To express the Arabidopsis enzyme in Escherichia coli, the entire coding region was subcloned into an expression vector. A cell-free extract of E. coli transformed with the recombinant plasmid, in the presence of NADPH and Mg2+, efficiently converted [14C]farnesyl diphosphate into squalene. On the other hand, in the absence of NADPH and the presence of Mn2+, the cell-free extract formed dehydrosqualene as a secondary product. Another E. coli extract expressing mouse squalene synthase showed the same activity as the Arabidopsis enzyme. Therefore, both the structure and reaction mechanism of squalene synthases are markedly conserved in taxonomically remote eukaryotes.

Immunohistochemical detection of advanced glycosylation end products within the vascular lesions and glomeruli in diabetic nephropathy

Numerous studies over the years have implicated advanced glycosylation end products (AGEs) in the pathogenesis of many of the complications of diabetes and normal aging. The recent development of specific antibodies against AGE-modified proteins has facilitated investigations on the formation and tissue distribution of AGEs. We used anti-AGE antibodies to localize AGEs within kidney specimens obtained from both diabetic and nondiabetic individuals. Immunohistochemical staining using anti-AGE antibody showed a high level of AGE accumulation in diabetic and aged vascular intima, particularly along the inner elastic layer of arteries. Positive staining also was observed within nodular and severe diffuse lesions of glomeruli as well as in hyaline deposits of arterioles. These data support a pathogenic role for advanced glycosylation in the renal complications of diabetes and aging.

nfxC-type quinolone resistance in a clinical isolate of Pseudomonas aeruginosa

Quinolone resistance gene nqr-T91 in a clinical isolate of Pseudomonas aeruginosa P1481 was cotransducible with catA1 in P. aeruginosa PAO. The nqr-T91 transductant, PKH-T91, was resistant to norfloxacin, imipenem, and chloramphenicol and showed less norfloxacin accumulation than the parent strain did. Loss of the 46-kDa outer membrane protein (D2) and an increase in the 50-kDa outer membrane protein in PKH-T91 were observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Lipopolysaccharides in the transductant were also changed. These alterations were considered to be related to lower levels of norfloxacin accumulation in PKH-T91. These genetic and biochemical properties suggested that an nfxC type of quinolone-resistant mutation occurred in a clinical isolate of P. aeruginosa P1481.

The structure of chicken liver xanthine dehydrogenase. cDNA cloning and the domain structure

The amino acid sequence of chicken liver xanthine dehydrogenase (EC 1.1.1.204) was determined by cDNA cloning and partial amino acid sequencing of the purified enzyme. The enzyme consisted of 1358 amino acids with calculated molecular mass of 149,633 Da. In order to compare the structure of the chicken and rat enzymes, limited proteolysis was performed with the purified chicken liver xanthine dehydrogenase. When the enzyme was digested with subtilisin, it was not converted from the NAD-dependent dehydrogenase type to the O2-dependent oxidase type, in contrast with the mammalian enzyme. However, the enzyme was cleaved mainly into three fragments in a manner similar to that for the rat enzyme at pH 8.2 (20, 37, and 84 kDa) and retaining a full complement of redox centers. The cleavage sites were identified by determination of amino-terminal sequences of the produced fragments. It was concluded that the 20-kDa fragment was amino-terminal, the 84-kDa fragment carboxyl-terminal, and the 37-kDa fragment an intermediate portion in the enzyme protein. On the other hand, when the enzyme was digested with the same protease at pH 10.5, the sample contained only the 20- and 84-kDa portions and lacked the 37-kDa portion. The resultant sample possessed xanthine dichlorophenol indophenol reductase activity, indicating that the molybdenum center remained intact. The absorption spectrum showed the sample was very similar to deflavo-enzyme. From these results and sequence analyses, the domain structure of the enzyme is discussed.

Mapping of the gene for human xanthine dehydrogenase (oxidase) (XDH) to band p23 of chromosome 2

Fluorescent in situ hybridization in combination with Q-banding revealed that the human xanthine dehydrogenase (XDH) gene is located on band p23 of chromosome 2.

Effects of alpha- and beta-arbutin on activity of tyrosinases from mushroom and mouse melanoma

The effects of alpha- and beta-arbutin on the activity of tyrosinases from mushroom and mouse melanoma were examined. alpha-Arbutin was synthesized from hydroquinone and starch using glucoside synthetase (GSase). beta-Arbutin inhibited both tyrosinase activities from mushroom and mouse melanoma. alpha-Arbutin inhibited only the tyrosinase from mouse melanoma, 10 times as strongly as beta-arbutin. The IC50 of alpha-arbutin was 0.48 mM and its inhibitory mechanism was speculated to be mixed type inhibition, while that of beta-arbutin was noncompetitive.