can enzymes work on nonspontaneous (endergonic) reactions?

The normal meaning of "enzyme" is that it's a catalyzes the reaction, meaning it affects the rate of reaction by findning a quicker route, but the equilibrium between of products and reactants are unchanged. So enzyme do not make unfavourable thermodynamically overall reactions favourable.

 

Things that do that exists in living cells, but that's not called enzymes, it's more active entities, that exploit another thermodynamic gradient to help another reaction, for it example ion gradients ca be exploited by membrane pumps, to make a cross membrane transport that would otherwise not be favourable. But once you add the ion gradient in the picture, the overall reaction is of course still favourable.

 

/Fredrik