IN-VITRO ASSEMBLY OF FAD, AMP, AND THE 2 SUBUNITS OF ELECTRON-TRANSFERRING FLAVOPROTEIN - AN IMPORTANT ROLE OF AMP RELATED WITH THE CONFORMATIONAL CHANGE OF THE APOPROTEIN

Electron-transferring flavoprotein from pig kidney is composed of four non-covalently bound components: alpha and beta subunits, flavin aden ine dinucleotide (FAD), and adenosine monophosphate (AMP), This paper reveals the pathway of assembly of the electron-transferring flavoprot ein. The holoprotein can be formed by two different pathways, (i) alph a+beta reversible arrow (alpha-beta), (alpha-beta)*+AMP reversible ar row (alpha-beta-AMP), (alpha-beta-AMP)* reversible arrow alpha-beta-A MP, alpha-beta-AMP+FAD reversible arrow holoprotein, (ii) alpha+beta r eversible arrow alpha-beta, alpha-beta+FAD reversible arrow alpha-beta -FAD, alpha-beta-FAD+AMP reversible arrow holoprotein, Here the presen ce and absence of asterisks distinguish different conformations with t he same composition, The monomeric forms of alpha and beta showed no s ignificant binding with FAD and AMP. AMP and FAD associated with diffe rent heterodimer forms which were formed as a result of weak binding b etween alpha and beta, The binding of alpha+beta+AMP was much faster t han that of alpha+beta+FAD because the rate of alpha+beta-->(alpha-bet a) was much faster than that of alpha+beta-->alpha-beta, The alpha-be ta-AMP complex associated with FAD rapidly, As a result, the binding o f FAD with the subunits is promoted by AMP, The alpha-beta-FAD complex associated with AMP much more slowly than the mixture of alpha and be ta, Thus the AMP binding with the subunits is inhibited by the precedi ng FAD binding.