Induction of chitinase and β-1,3-glucanase in Parthenocissus quinquefolia cells cultured in vitro

Chitin, chitosan and peptidoglycan induced chitinase (EC 3. 2. 1. 14) activity in Parthenocissus quinquefolia cells cultured in vitro, while cellulose did not. The real inducers seemed to be oligomers released from the large size polymers by hydrolytic enzymes secreted into the medium during the cell growth and division. This effect was mimicked by the addition to the medium of a partially purified Parthenocissus chitinase/lysozyme (EC 3. 2. 1. 17), which was also able to hydrolyse chitosan. Oligomers of chitin and of chitosan induced the activity to the same level and with the same time course, while peptidoglycan oligomers induced less activity. Oligomers also induced β-1,3-glucanase (EC 3. 2. 1. 6) activities. The changes with time of both activities and the relative effects of the three kinds of polymers suggested that the induction of both enzymes involves a common element early in the signal pathway.     

Oxalate accumulation from citrate by Aspergillus niger. I. Biosynthesis of oxalate from its ultimate precursor.

Carbon-14 was incorporated from citrate-1,5-14C, glyoxylate-14C(U), or glyoxylate-1-14C into oxalate by cultures of Aspergillus niger pregrown on a medium with glucose as the sole source of carbon. Glyoxylate-14C(U) was superior to glyoxylate-1-14C and citrate-1,5-14C as a source of incorporation. By addition of a great amount of citrate the accumulation of oxalate was accelerated and its maximum yield increased. In a cell-free extract from mycelium forming oxalate from citrate the enzyme oxaloacetate hydrolase (EC3.7.1.1) was identified. Its in vitro activity per flask exceeded the rate of in vivo accumulation of oxalate. Glyoxylate oxidizing enzymes (glycolate oxidase, EC1.1.3.1; glyoxylate oxidase, EC1.2.3.5;NAD(P)-dependent glyoxylate dehydrogenase; glyoxylate dehydrogenase, CoA-oxalylating, EC1.2.1.7) could not be detected in cell-free extracts. It is concluded that in cultures accumulating oxalate from citrate after pregrowth on glucose, oxalate arises by hydrolytic cleavage of oxaloacetate but not by oxidation of glyoxylate.     

Long chain ceramides activate protein phosphatase-1 and protein phosphatase-2A. Activation is stereospecific and regulated by phosphatidic acid.

The search for potential targets for ceramide action led to the identification of ceramide-activated protein phosphatases, which include protein phosphatase-2A (PP2A) and protein phosphatase-1 (PP1) with roles in regulating apoptosis and cell growth. Thus far, in vitro studies on ceramide-activated protein phosphatases have been restricted to the use of short chain ceramides, limiting the extent of mechanistic insight. In this study, we show that the long chain D-erythro-C18-ceramide activated PP2A (AB'C trimer), PP2Ac (catalytic subunit of PP2A), and PP1gammac and -alphac (catalytic subunits of PP1gamma and -1alpha isoforms, respectively) 2-6-fold in the presence of dodecane, a lipid-solubilizing agent, with 50% maximal activation achieved at approximately 10 microM D-erythro-C18-ceramide. The diastereoisomers of D-erythroC18-ceramide, D-threo-, and L-threo-C18-ceramide, as well as the enantiomeric L-erythro-C18-ceramide, did not activate PP1 or PP2A, but they inhibited PP1 and PP2A activity. The addition of phosphatidic acid decreased the basal activity of PP1c but also increased the stimulation by D-erythro-C18-ceramide from 1.8- to 2. 8-fold and decreased the EC50 of D-erythro-C18-ceramide to 4.45 microM. The addition of 150 mM KCl decreased the basal activity of PP1 and the dose of D-erythro-C18-ceramide necessary to activate PP1c (EC50 = 6.25 microM) and increased the ceramide responsiveness up to 10-17-fold. These studies disclose stereospecific activation of PP1 and PP2A by long chain natural ceramides under near physiologic ionic strengths in vitro. The implications of these studies for mechanisms of ceramide action are discussed.     

Gluconate accumulation and enzyme activities with extremely nitrogen-limited surface cultures of Aspergillus niger

Batch cultures of Aspergillus niger grown from conidia on a medium with high C/N ratio accumulated gluconate from glucose with a yield of 57%. During almost the whole time of accumulation there was no net synthesis of total protein in the mycelium but the activity per flask and the specific activity of glucose oxidase (EC 1.1.3.4) in mycelial extracts increased whereas both values decreased for glucose dehydrogenase (EC 1.1.99.10) gluconate 6-phosphatase (cf. EC 3.1.3.1, 3.1.3.2), gluconokinase (EC 2.7.1.12), glucose 6-phosphate and phosphogluconate dehydrogenases (EC 1.1.1.49, EC 1.1.1.44), phosphoglucomutase (EC 2.7.5.1), and most enzymes of the Embden-Meyerhof pathway and the tricarboxylic acid cycle. Gluconate dehydratase (EC 4.2.1.39), gluconate dehydrogenase (EC 1.1.99.3) and enzymes of the Entner-Doudoroff pathway could not be detected. By cycloheximide the increase of glucose oxidase activity was inhibited. It is concluded that the high yield of gluconate was due mainly to the net (de novo) synthesis of glucose oxidase which occurred during protein turnover after the exhaustion of the nitrogen source, and which was not accompanied by a net synthesis of the other enzymes investigated. Some gluconate may also have been formed by hydrolytic cleavage of gluconate 6-phosphate.Abbreviations GOD glucose oxidase - GD glucose dehydrogenase - PP pentose phosphate - EM Embden-Meyerhof - TCA tricarboxylic acid     

Interactions of arterial cells. Studies on the mechanisms of endothelial cell modulation of cholesterol metabolism in co-cultured smooth muscle cells

Fluid phase interactions between arterial endothelial cells (EC) and smooth muscle cells (SMC) have been studied in vitro to assess the regulation of lipid metabolism in SMC (Hajjar, D. P., Falcone, D. J., Amberson, J. B., and Hefton, J. M. (1985) J. Lipid Res. 26, 1212-1223; Davies, P. F., Truskey, G. A., Warren, H. B., O'Connor, S. E., and Eisenhaure, B. H. (1985) J. Cell Biol. 101, 871-879). To identify EC-derived agonists which may modulate cholesterol metabolism in co-cultured SMC, we assessed the role of EC-derived eicosanoids and platelet-derived growth factor (PDGF) in the regulation of cholesteryl ester (CE) hydrolysis in SMC. The major eicosanoids synthesized by EC include PGI2 and 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) and, to a lesser extent, prostaglandin E2. Exogenously added PGI2 and 12-HETE stimulated CE hydrolytic activity in SMC by 49 and 35%, respectively, when co-cultured with aspirin-treated EC. Aspirin-treated EC when co-cultured with SMC did not stimulate CE hydrolytic activity in SMC, as was the case with non-aspirin-treated EC, suggesting a role of eicosanoids in the regulation of cholesterol metabolism. Other humoral agents derived from EC such as PDGFc stimulated CE hydrolytic activity almost 2-fold in SMC cultured alone or co-cultured with EC. Aspirin-treated EC, incubated with 10 ng/ml PDGF, did not stimulate CE hydrolytic activity in co-cultured SMC. These results suggest that growth factor-promoting activity may enhance CE hydrolysis via the PGI2-cyclic AMP-CE hydrolysis cascade. This hypothesis supports our observations that PDGF stimulates PGI2 production in SMC. Elevated PGI2, in turn, can stimulate CE hydrolysis in these cells. Our findings suggest that the regulation of cholesterol metabolism in SMC can involve, at least in part, growth factors and EC-derived eicosanoids. These may play a central role in the regulation of hemostasis and the inflammatory response.     

Organophosphate detoxicating hydrolases in different vertebrate species

Phosphorylphosphatase activities in various organs of vertebrate species from different classes were determined using a spectrophotometric assay for paraoxonase (EC 3.1.1.2) and a potentiometric assay with a fluoride sensitive electrode for DFPase (EC 3.8.2.1). Temperature-dependent inactivation experiments, an extended interpretation of mixed substrate studies and activity distribution patterns confirm that in vertebrate tissue at least two different enzymes are responsible for hydrolytic detoxication of paraoxon and DFP. Total organophosphate detoxicating phosphorylphosphatase activity of a certain animal species is shown to be the major determinant for differences between the inhibitory potency of organophosphorus compounds on the animal's target enzymes in vitro and organophosphate toxicity in vivo.     

Occurrence of phytoalexins and other putative defense-related substances in uninfected parsley plants

Considerable amounts of the following substances were found in uninfected parsley (Petroselinum crispum) cotyledons: furanocoumarins, the putative phytoalexins of this and some related plant species, two enzymes of the furanocoumarin pathway (S-adenosyl-L-methionine: xanthotoxol and S-adenosyl-L-methionine: bergaptol O-methyltransferases), two hydrolytic enzymes (1,3--glucanase, EC 3.2.1.39, and chitinase, EC 3.2.1.14), and pathogenesis-related proteins. The furanocoumarins and the methyltransferase activities reached their highest levels at the onset of cotyledon senescence as the hydrolytic enzymes increased from low to relatively high activity values. The relative amounts of pathogenesis-related proteins 1 and 2, as well as the corresponding mRNAs, also increased markedly. Two enzymes of general phenylpropanoid metabolism, L-phenylalanine ammonia-lyase and 4-coumarate: CoA ligase, decreased in activity in a biphasic fashion during cotyledon development. At all developmental stages, the levels of these putative defense-related agents in total cotyledon extracts were too high to enable detection of, possibly, additional changes upon infection with zoospores of Phytophthora megasperma f. sp. glycinea, a fungal pathogen to which parsley shows a non-host, hypersensitive resistance response.Abbreviations BMT S-adenosyl-L-methionine: bergaptol O-methyltransferase (EC 2.1.1.-) - 4CL 4-coumarate: CoA ligase (EC 6.1.1.12) - CMT S-adenosyl-L-methionine: caffeate O-methyltransferase (EC 2.1.1.-) - PAL L-phenylalanine ammonia-lyase (EC 4.3.1.5) - PR pathogenesis-related - XMT S-adenosyl-L-methionine: xanthotoxin O-methyltransferase (EC 2.1.1.-)     

Hydrolytic activities of anaerobic fungi from wild blue bull (Boselaphus tragocamelus)

The anaerobic fungi play an active role in the plant fibre degradation by producing a wide array of potential hydrolytic enzymes in the rumen. In present study, 12 anaerobic fungal strains were isolated from the faecal samples of wild blue bull, and identified as species of Piromyces, Anaeromyces, Orpinomyces and Neocallimastix based on their morphological characteristics. Isolate WNG-12 (Piromyces sp.), showed maximum filter paper cellulase (23 mIU ml(-1)) and xylanase (127 mIU ml(-1)) activity, while WNG-5 (Piromyces sp.) showed maximum carboxymethyl cellulase activity (231 mIU ml(-1)). Based on the results obtained, it can be stated that Piromyces sp. WNG-12 may be a promising isolate in utilizing fibre rich diets in the rumen as evidenced by the production of hydrolytic enzymes in vitro.     

Acid and alkaline phosphatases of Capnocytophaga species. I. Production and cytological localization of the enzymes

The two hydrolytic enzymes, acid (AcP; EC 3.1.3.2) and alkaline (AlP; EC 3.1.3.1) phosphatase, of the three types species of Capnocytophaga were examined. Both enzymes were produced constitutively, with their activity highest in C. ochracea strain 25. These two degradative enzymes (approximately 10% of the total activity) were released into the growth medium during the latter stages of growth, both as soluble and membrane-bound enzymes. When grown in the presence of high concentrations of organic phosphates, the synthesis and expression of AcP and AlP was unaltered. Cyto- and immuno-chemical localization situated the phosphatases in the periplasmic space, at the cell surface, and in membranous vesicles.     

Cyanobacterial PPP family protein phosphatases possess multifunctional capabilities and are resistant to microcystin-LR

The structural gene for a putative PPP family protein-serine/threonine phosphatase from the microcystin-producing cyanobacterium Microcystis aeruginosa PCC 7820, pp1-cyano1, was cloned. The sequence of the predicted gene product, PP1-cyano1, was 98% identical to that of the predicted product of an open reading frame, pp1-cyano2, from a cyanobacterium that does not produce microcystins, M. aeruginosa UTEX 2063. By contrast, PP1-cyano1 displayed less than 20% identity with other PPP family protein phosphatases from eukaryotic, archaeal, or other bacterial organisms. PP1-cyano1 and PP1-cyano2 were expressed in Escherichia coli and purified to homogeneity. Both enzymes exhibited divalent metal dependent phosphohydrolase activity in vitro toward phosphoserine- and phosphotyrosine-containing proteins and 3-phosphohistidine- and phospholysine-containing amino acid homopolymers. This multifunctional potential also was apparent in samples of PP1-cyano1 and PP1-cyano2 isolated from M. aeruginosa. Catalytic activity was insensitive to okadaic acid or the cyanobacterially produced cyclic heptapeptide, microcystin-LR, both potent inhibitors of mammalian PP1 and PP2A. PP1-cyano1 and PP1-cyano2 displayed diadenosine tetraphosphatase activity in vitro. Diadenosine tetraphosphatases share conserved sequence features with PPP family protein phosphatases. The diadenosine tetraphosphatase activity of PP1-cyano1 and PP1-cyano2 confirms that these enzymes share a common catalytic mechanism.     

Establishment and biochemical characterization of tamarillo (<Emphasis Type="Italic">Solanum betaceum</Emphasis> Cav.) embryogenic cell suspension cultures

Somatic embryogenesis (SE) is an important biotechnological tool with great potential for large-scale cloning. In Solanum betaceum Cav. (tamarillo), embryogenic (EC) and non-embryogenic (non-EC) cells can be obtained from the same explant on auxin-containing medium, making this system ideal for the evaluation of biochemical changes occurring during embryogenic induction. Liquid cultures offer additional possibilities for the analysis of factors controlling SE induction, and the main objectives here were the establishment of cell suspensions and the characterization of the extracellular protein profiles in EC and non-EC cultures. Growth kinetics of liquid cultures, starting with different amounts of EC or non-EC callus or with different weight per volume ratios, were analyzed. Embryogenic suspension cultures were efficiently established starting with 40 mg of cells in 20 mL of liquid medium. Mass spectrometry and fluorometric techniques were employed to identify extracellular proteins, their hydrolytic activity, and the main classes of proteases secreted into the media of EC or non-EC cultures. Extracellular protein profiles revealed quantitative and qualitative differences between EC and non-EC suspension cultures, mainly for several hydrolytic enzymes, such as glucanases and xylanases. Proteolytic activity analysis found serine proteases, aspartic proteases, and metalloproteases in EC cultures, whereas serine proteases were dominant in non-EC lines. For the first time, a protocol for the growth of tamarillo EC and non-EC suspensions was achieved. Moreover, the comparison of protein profiles between EC and non-EC lines showed pronounced differences in the proteolytic and glycolytic enzymes secreted.     

Activity of cell wall-associated enzymes in ripening olive fruit

Enzymatically active cell wall isolaled from olive (Olea europaea) fruit was employed Hi investigate some hydrolytic enzymes bound to the cell wall and the changes in these during ripening. Seven glycosidases. β-glucosidase (EC 3.2.1.21) α-galactosidase (EC 3.2.1.22). β-galactosidase (EC 3.2.1.23). α-arabinosidase (EC 3.2.1.55), α-mannosidase (EC 3.2.1,24). β-xylosidase (EC 3.2.1.37) and β-N-acetylglucosamidase (EC 3.2.1.30). as well as Cx-cellulase (EC 3.2.1.4) and endo-polygalacturonase (EC 3.2.1.15). were identified in the cell wall preparation, at four stages of ripeness (mature green. changing colour, black and black-ripe). Activities of all these cell wall-associated enzymes fionicallv and covalently linked) were determined either by cell wall incubation with artificial substrate or after extraction from the cell wall with buffers of high salt concentration (Cx-cellulase). and were compared to those of forms solubilized from acetone powders with 500 nM citrate buffer (cytoplasmic and/or apoplastic plus ionically hound to cell wall) In general, the activities of low ionic strength buffer-soluble enzymes were found to be much higher than those of the bound enzymes. The bound enzymes are present in the fruit at the green colour stage, whereas the activities of the soluble enzymes only increased from the changing colour stage onwards. The tenacity of binding of enzymes to the wall was investigated by treating the walls with high salt and measuring residual activity. The nature of the ionic and covalent binding and the changes during ripening were also established for wall-hound glycosidase During ripening there was a marked change in the percentages of covalently- and tonically linked activities of β-glucosidase and β-galaclosidase: al the changing colour stages about 75–80% of the bound active in was present in high ionic strength buffer while al the black-ripe stage it was only 15–20. A possible role for these cell wall degradative enzymes in olive softening is discussed.     

The first glycosynthase derived from an inverting glycoside hydrolase

Reducing end xylose-releasing exooligoxylanase (Rex, EC 3.2.1.156) is an inverting GH that hydrolyzes xylooligosaccharides (> or = X3) to release X1 at their reducing end. The wild-type enzyme exhibited the Hehre resynthesis hydrolysis mechanism, in which alpha-X2F was hydrolyzed to X2 and HF in the presence of X1 as an acceptor molecule. However, the transglycosidation product (X3) was not detectable in the reaction. To convert reducing end xylose-releasing exooligoxylanase to glycosynthase, derivatives with mutations in the catalytic base (Asp-263) were constructed by saturation random mutagenesis. Nine amino acid residue mutants (Asp-263 to Gly, Ala, Val, Thr, Leu, Asn, Cys, Pro, or Ser) were found to possess glycosynthase activity forming X3 from alpha-X2F and X1. Among them, D263C showed the highest level of X3 production, and D263N exhibited the fastest consumption of alpha-X2F. The D263C mutant showed 10-fold lower hydrolytic activity than D263N, resulting in the highest yield of X3. X2 was formed from the early stage of the reaction of the D263C mutant, indicating that a portion of the X3 formed by condensation was hydrolyzed before its release from the enzyme. To acquire glycosynthase activity from inverting enzymes, it is important to minimize the decrease in F(-)-releasing activity while maximizing the decrease in the hydrolytic activity. The present study expands the possibility of conversion of glycosynthases from inverting enzymes.     

Roles of histidine residues in plant vacuolar H(+)-pyrophosphatase

Vacuolar proton pumping pyrophosphatase (H(+)-PPase; EC 3.6.1.1) plays a pivotal role in electrogenic translocation of protons from cytosol to the vacuolar lumen at the expense of PP(i) hydrolysis. Alignment analysis on amino acid sequence demonstrates that vacuolar H(+)-PPase of mung bean contains six highly conserved histidine residues. Previous evidence indicated possible involvement of histidine residue(s) in enzymatic activity and H(+)-translocation of vacuolar H(+)-PPase as determined by using histidine specific modifier, diethylpyrocarbonate [J. Protein Chem. 21 (2002) 51]. In this study, we further attempted to identify the roles of histidine residues in mung bean vacuolar H(+)-PPase by site-directed mutagenesis. A line of mutants with histidine residues singly replaced by alanine was constructed, over-expressed in Saccharomyces cerevisiae, and then used to determine their enzymatic activities and proton translocations. Among the mutants scrutinized, only the mutation of H716 significantly decreased the enzymatic activity, the proton transport, and the coupling ratio of vacuolar H(+)-PPase. The enzymatic activity of H716A is relatively resistant to inhibition by diethylpyrocarbonate as compared to wild-type and other mutants, indicating that H716 is probably the target residue for the attack by this modifier. The mutation at H716 of V-PPase shifted the optimum pH value but not the T(1/2) (pretreatment temperature at which half enzymatic activity is observed) for PP(i) hydrolytic activity. Mutation of histidine residues obviously induced conformational changes of vacuolar H(+)-PPase as determined by immunoblotting analysis after limited trypsin digestion. Furthermore, mutation of these histidine residues modified the inhibitory effects of F(-) and Na(+), but not that of Ca(2+). Single substitution of H704, H716 and H758 by alanine partially released the effect of K(+) stimulation, indicating possible location of K(+) binding in the vicinity of domains surrounding these residues.     

Enzyme modification by natural chemical chaperons of microorganisms

We demonstrated for the first time that alkylhydroxybenzenes (the d1 microbial autoregulatory factors involved in stress responses of cells) are capable of stabilizing enzymes in aqueous media and increasing their catalytic activity. The stabilizing effect of a chemical analogue of alkylhydroxybenzenes, C7-AHB, was established in in vitro studies with enzymes of microbial origin: a protease produced by Bacillus licheniformis, cellulase produced by Trichoderma viride, and alpha-amylase produced by Bacillus subtilis. This effect manifested itself in considerable extension of the temperature and pH ranges of the enzymatic activity. The modulation of the catalytic activities of the stabilized enzymes depended on the C7-AHB concentration and on the time of preincubation of the complexes obtained. We demonstrated that not only enzymes but also their polymeric substrates formed complexes with C7-AHB, and this also significantly influenced the efficiency of hydrolytic reactions. We also conducted comparative studies on the efficiency of hydrolytic reactions in systems in which the structure of enzymes and/or substrates was modified with C7-AHB.     

Microbial hydantoinases – industrial enzymes from the origin of life?

Hydantoinases are valuable enzymes for the production of optically pure d- and l-amino acids. They catalyse the reversible hydrolytic ring cleavage of hydantoin or 5′-monosubstituted hydantoins and are therefore classified in the EC nomenclature as cyclic amidases (EC 3.5.2.). In the EC nomenclature, four different hydantoin-cleaving enzymes are described: dihydropyrimidinase (3.5.2.2), allantoinase (EC 3.5.2.5), carboxymethylhydantoinase (EC 3.5.2.4), and N-methylhydantoinase (EC 3.5.2.14). Beside these, other hydantoinases with known metabolic functions, such as imidase and carboxyethylhydantoinase and enzymes with unknown metabolic function, are described in the literature and have not yet been classified. An important question is whether the distinct hydantoinases, which are frequently classified as l-, d-, and non-selective hydantoinases depending on their substrate specificity and stereoselectivity, are related to each other. In order to investigate the evolutionary relationship, amino acid sequence data can be used for a phylogenetic analysis. Although most of these enzymes only share limited sequence homology (identity<15%) and therefore are only distantly related, it can be shown (i) that most of them are members of a broad set of amidases with similarities to ureases and build a protein superfamily, whereas ATP-dependent hydantoinases are not related, (ii) that the urease-related amidases have evolved divergently from a common ancestor and (iii) that they share a metal-binding motif consisting of conserved histidine residues. The difference in enantioselectivity used for the classification of hydantoinases on the basis of their biotechnological value does not reflect their evolutionary relationship, which is to a more diverse group of enzymes than was assumed earlier. This protein superfamily probably has its origin in the prebiotic conditions of the primitive earth. Received: 24 August 1998 / Received revision: 9 November 1998 / Accepted: 21 November 1998     

A study of the effect on nucleophilic hydrolytic activity of pancreatic elastase, trypsin, chymotrypsin, and leucine aminopeptidase by boronic acids in the presence of arabinogalactan: a subsequent study on the hydrolytic activity of chymotrypsin by boronic acids in the presence of mono-, di-, and trisaccharides

The hydrolytic activity of trypsin, chymotrypsin, elastase, and leucine aminopeptidase, is inhibited by different boronic acids. However, all the enzymes are inhibited by the compound CbzAla(boro)Gly(OH)(2). Therefore, these additives can control the nucleophilic hydrolytic activity of these enzymes.     

Comparative characteristics of cyclodextrin glycosyltransferases from various groups of microorganisms]

Cyclodextrin glycosyltransferases (CGT-ase, 1.4-alpha-glucanotransferase, cyclizing, EC 2.4.1.19) produced by some thermophilic, alkalophilic and mesophilic bacterial strains, were isolated and characterized. It was shown that thermophilic and mesophilic CGT-ases represent a mixture of alpha-, beta- and gamma-cyclodextrins (CD), alpha-cyclodextrin being the predominant component. Alkalophilic enzymes produce only beta-CD and are able to produce CD not only from starch but also from maltose, melibiose, maltotriose, amylose and amylopectin. The optimal conditions for the catalytic activity of the enzymes were determined. It was found that calcium, magnesium and zinc ions have a beneficial effect on the specific activity of these enzymes. The amino acid composition of the enzymes was studied.     

TIMAP is a positive regulator of pulmonary endothelial barrier function

TGF-beta-inhibited membrane-associated protein, TIMAP, is expressed at high levels in endothelial cells (EC). It is regarded as a member of the MYPT (myosin phosphatase target subunit) family of protein phosphatase 1 (PP1) regulatory subunits; however, its function in EC is not clear. In our pull-down experiments, recombinant TIMAP binds preferentially the beta-isoform of the catalytic subunit of PP1 (PP1cbeta) from pulmonary artery EC. As PP1cbeta, but not PP1calpha, binds with MYPT1 into functional complex, these results suggest that TIMAP is a novel regulatory subunit of myosin phosphatase in EC. TIMAP depletion by small interfering RNA (siRNA) technique attenuates increases in transendothelial electrical resistance induced by EC barrier-protective agents (sphingosine-1-phosphate, ATP) and enhances the effect of barrier-compromising agents (thrombin, nocodazole) demonstrating a barrier-protective role of TIMAP in EC. Immunofluorescent staining revealed colocalization of TIMAP with membrane/cytoskeletal protein, moesin. Moreover, TIMAP coimmunoprecipitates with moesin suggesting the involvement of TIMAP/moesin interaction in TIMAP-mediated EC barrier enhancement. Activation of cAMP/PKA cascade by forskolin, which has a barrier-protective effect against thrombin-induced EC permeability, attenuates thrombin-induced phosphorylation of moesin at the cell periphery of control siRNA-treated EC. On the contrary, in TIMAP-depleted EC, forskolin failed to affect the level of moesin phosphorylation at the cell edges. These results suggest the involvement of TIMAP in PKA-mediated moesin dephosphorylation and the importance of this dephosphorylation in TIMAP-mediated EC barrier protection.