Bisubstrate enzyme reaction kinetics - (Aug/13/2014 )

I understand that for the bisubstrate enzyme catalyzed reactions involving formation of ternary complex, increasing the substrate-2 concentration also increases V-max and Km for substrate-1. I can understand the effect on V-max logically, but can anyone explain why should increasing substrate-2 should increase the Km for sustrate-1?

the second substrate causes a conformational change in the enzyme which affects the active site for the first substrate.