Transductional andStructural Principles oftheMitochondrial Transducing Unit

The electromechanochemical modelhas beenreformulated totakeaccountofthecloseconnection betweenenergycouplingandcatalysis. Incatalysis the protein isprogrammedtoutilize thermalenergytopro- ducelocalstrains inthecatalytic cavityandtogenerate conformational statesthatfavorsubstrate - product conversion. Energycouplinginvolves transfer ofvibra- tional energythroughtheprotein. Underlying thesetwo energytransductional maneuversistheconceptofapul- satingproteincapable ofredistributing electromechano- chemicalpotential energyinaprogrammedfashion. The mitochondrial supermolecule hasbeendefined, andithas beenshownhow thesupermolecule conceptrationalizes thecouplingoptions, thestoichiometry ofthecoupling complexes, andthemultistep- character ofelectron trans- fer. Thesalient features oftheelectromechanochemical (EMC) modelofmitochondrial energy transduction (1-3) previously proposed byusare: thetransducing unit(supermolecule) isa molecular machine thatmanipulates chemical andelectro- mechanochemical energy; there isatransfer ofvibrational energy fromexergonic toendergonic sites ofthesupermolecule viaa linkage system; energyistransferred inquantized packets called theconformon; andexergonic andendergonic sites arecoupled viaanelectric field. Thismodel, whichwas arrived atbyanapriori method, provides arational basis for integrating theknownfacts aboutmitochondrial coupling. We arenow proposing threenew criteria bywhichthe validity ofthetransductional principles oftheEMC model canbeassessed. (a)Since energy coupling isinextricably tied intocatalysis, theEMC modelshould alsobecapable of extension tothemechanism ofcatalysis. (b)Thestructure ofa transducing unit aswell asitscontrol features mustaccurately reflect andtranslate thetransducing principles. Therefore knowledge ofthetransducing principles should leadtoan accurate prediction ofboththestructural andcontrol prin- ciples. (c)Since itishighly likely thatthemechanism of energy coupling isuniversal inbiological energy-transducing systems (4), itwouldbepredictable thattheEMC model should beapplicable tosystems other thanthemitochondrion. Inaseries ofpapers ofwhichthis isthefirst, weintend to describe ourprogress indelineating thestructural andcontrol principles ofthemitochondrial transducing unit(5)andin extending theEMC modeltocatalysis ingeneral aswellas tothemuscle contractile system(Ji, S.andGreen, D.E., manuscript inpreparation). Inthepresent communication, weshall restate themito- chondrial transducing principles inthenewformdictated by theinsights acquired inextending theEMC model tocatalysis, andthenspecify thestructural principles ofthemitochondrial transducing unit.