How does accumulation of end-products affect enzyme activity?

Accumulation of end-products inhibits enzyme activity. 

When too many end-products accumulate, they crowd the active sites of the enzymes. This leaves very few free active sites on the enzyme that substrate molecules can bind to, thereby preventing excessive production of end-products and conserving resources within the cell. This phenomenon is called feedback inhibition. It acts as a regulatory mechanism that helps to maintain homeostasis.