TheBiophysicalSociety of Japan General IncorporatedAssociation Crowding" infiuences thc dynamics ofmolecules themse]ves. In this study, we censider the influcnces of molecular crowding on the signaling using a lattice gas model, which simplifies G-protein-mediated signaling cascade on ccll membrane and realizes the excluded vo)umc effect or moleeu]es. In thc model, three types ofpToteins/ Receptor, Signaling protein (hereafteT Sprotein), and TaTget protein (hereafter TargeO are tukeri into

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... nt, and each protein walks randomly on the two dimensional hexagonal lattice which rcprescnts the cell membrane. PToteins aTe assumed to transmit the sigllal -,ith thc process; Receptor -S-protein -Target, by the direct contact aL thc acljacent sites. By the simulation, we obtain the relation among the densjty of Receptor, the density of S-protcin, the jeint probability of Target to the membrane, and activation frequency with which S-proteins activate Target, and find that i) the maximum activation freq"ency is realized when most sites is occupied by the proteins, and ii) proteins locally fbnn characteristic spatial structure centering around Target. These results indicate that molecular crowding assists the effective transmiL of signal in living cells. ], Hiroshi lshiguroL (i Departments oj' Hkman Nittnition and Gastroenteroiogy, Nitgoya Uhive]'siij, G]'aduate School qf'Medicine, Japan, 2Department qfPharmacotogy, Schoot qfMedicine, Keio Univeii'itv. , Japan, 3Facutty ofL(fe St,iences, the Univengic.}' (tf'MbnehesteL UK) fntensity showed that the variance of the sigrral intensity increascd as the tota1 number ef rnolecuies decreased. The prebability that the $ignal intensity was reduced to O% increased as the variance incTeased, where the extinction probability increased as the reaction cascade reached to lower steps, Wc discuss the role of the stochastic cascade reaction as fluctuatjon pTopagation of ampTification and extinction ef the signal i'rom the viewpoint of information processing. IFIs4s wcbcrnu[[ukn:jeefitauemms*vFv-oE7-Jvopsust Weber's La}v in Autocatalytic Reaction Netyi'orks Masayo Inouei, Kunihiko Kaneko2 (i CMC Osaka Uhiv., 2Grad. Sch. Arts and Sci., Unii,. qfTk)k}'o) Bielogjcal responses often obey Weber's law, according to which the magnitude ofthe response depends only on the fold change in the extenia] input. Recently, Weber's law was also observed to be obeyed by cellulur responses in microorganisms, We demonstrate that a sirnple system of t-,o variables with autocata]ytic reactions exhibits an adaptive responsc according to Weber's Iaw when a chemical is slowly synthesized by thc reaction from a faster influx process. We also show that coupling or onc more variab1e to the reaction lead to escillatory adaptation ebeying Weber's taw. Sueh an oscil]atory adaptation has often becn observed in experiments, in cAMP eoneentration in Dico,ostelium eeTTs, for exainple. In contrast, theoretical models for the oscillatory adaptation have rareEy been explored. Weber's law is usually obeyed in an autocatalytic reaction system with timcscale difTeTences, without any special desigll or tuning of the parameters. Considering the simplicity and ubiquity of the autocata]ytic process, our proposed mechanism is cxpected to be eommonty obsen'ed in biological reactions. Panereatic duct epithetium produces HCOi'-rich (-・140 mM) fluid secretion. To investigate the ce]luTar and molecular mechunisms, we have constructed a simulation model ef panereatic duct cell using MATLAB/Simulink. Na' -HC03' cotransport and Na'-H' cxchange in the basotateral membrane ",ork foT HC03' aecuinulation. HC03' secretion aeross thc apieal rnembrane is mediatedbyCFTR(cysticfibrosistransrnembraneeonductanceregulatoT)anion channcl and SLC26A6 ]Ct'-2HC03' exchange. The luminal volume is small <cell / tumen == 10 : 1) and fixed. Luminal ion composition is altered by fiuid secretionandthesameamountoCfluidiscxcrctedfromthe]umen,Atthesteady state, HC03' concentratien ef the secreted fiuid equals luminal HCO]' concentration ([HCO]']L). Our previous measurement of intracellular Cl' conccntratien jn guinea-pig pancreatic duct suggested that basotateral Cl'-HCO]' exchange (AEbD was inhibited by cAMP stimulation. Ill the presellt study we examined the cffects of AEbt inhibitjon en HC03' secretion in our siinulation model, When AEhi was not inhibited (same to basaHeveT), the steady-state [HCO]']L was --97 mM. When AEbi activity was Teduced to 50% and lO%, the steady-state [HCO]'1i. was --114 mM and --139 mM respcctively. The$e data suggest that inhibition of AEbi is necessary for HCO]'-rich fiuid secretion by pancreatie duct. IF1536P74 MasashiKajita Biosci, & Biotech tos(vtitJvm{MEM=taBrcpmLffi[es[t6ttsemmsnxtr-FcotsttERo]e of a stechastic cascade reactiolt in the signal trallsduction s},stem froin the viewpoint of information processing i, Kumiko Sakata-Sogawa]2, Makio Tokunagai'2 (iGrad. Sch. 7blyo inst. 7lech., 2RcaL RmaN) Dynamic features in signaling pathways are ef panicutar interest to understanding the dynamic and variety functions ofcells. Systems biolegy has contributed to clarifying properties efcombined motifs, such as the MAP kinase cascade. and of stationary responses. However, relatii,ely little is known about the dynamic featuT ¢ ef the eascade. It has been reported LhaL a sLochastic signa] transduction system has an optimal number of molecules for signal amplitlcation and discrimination betwcen truc and crror signal. The meclianism is explained that the interplay betu'een stochasticity due to a smatt number of molecules and the effect of signaHess. The function of a stechastic cascade reaction in the signal transduction system from the viewpoint of infonnaLion processing is left to be further invcstigatcd. In this study, we carried out simulations of a sigrialing cascade using stochastic differentia] equations and quantified the infonnation processing abiTity. The signal intensity was obtained as the ratjo of active moiecules at each reaction step. Analysis oC thc sigrial 1Fl612 Utilizing history for robust informatioll processing to noise by intracelluiar reactions Atsushi Kamimurai, Tetsuya Kobayashii'2 (ifnstitute of industi'ial Seience, the LJhiversin. ' qf fblp,o, 2IlllESTO, rs7) Inherentlystochasticnaturcot'chemicalreactionsinducesapparentnoisysignals in cellular processcs. While reeent direct expetimentalobsers,ations suppert this, it suggests that they employ a differentmechanism frem conventional humanmade machineries in which mucheffort has been donc to rcduce the noise in signalsfbrpreciseinforrnationtransmissionandprocessing,Onepossiblewayto explainthc consistency between their sharp responses and the noisy signals isthat celts utilize the inibrmation not only of instantancous signalsbut also of their histories. However, it is not fu]ly understood whatkind of structures and mechanisms of chemical reactions can exploitthe infoirnatioll that the history has. To address this problem, we point out here, in the proccssing fiowfrom environmental signals to intracellular networks, thatreconstructing intbrmation orthe staning point is possible at theend point ofthe flow, by using the temporal historyoi'sjgnals,eventhoughinstantaneoussignalsattheintermediatestepsare very noisy. In particular, we clarify that, by measuring mutual inforniation, certain structure of reactions. which can implement dynamic Bayesianinformation processing, determines the inaximum limit of such decoding. In addition to the temporal processing, we also consider spatiatdegree of freedom to investigate the effects for robust responses. IF1624P75 Shinsuke Uda (LGrad. Sch. JSDIn cellular signal transduction, information in external stimulus is usually coded as temporal strength of signaling activities. However, the uncertainty of information transmission has been pooTTy investigated. We apply Shannon's information theory to eellular signal transductien. A pathway of signaljng netsvork is regarded as a cornmunication channe]. The amount of information that can be reliably transmitted oi,er the cornmunicatioll chaimel is measured by mutual information. And, the upper bound of mutual infonnation against input distribution is the channei capacity.We examined the mutuat information of ERK signaLing network between stimulation and molecule er between molecules in PC12 cell. ERK signaling network consists of aEfircfiEMLIk PC12 maMa) ERK VtiV-JVtfiif*v F7-ooneMMutua]informatio"analysisofERKsignalingnetworkinPC cell i, Takeshi Saitoi, NaohiTe Takahashi2, Shinya Kurodai'2'3 Sci., Univ. Tblyo, 2Grad, Sch. Frontier Sci., e7iiv, 7bdy'e, ]CRESZ -S44 -NII-Electronic