You have isolated a previously unstudied protein, identified its complete structure in detail, and determined that it catalyzes the breakdown of a large substrate. you notice it has two binding sites. one of these is large, apparently the bonding site for the large substrate; the other is small, possibly a binding site for a regulatory molecule. what do these findings tell you about the mechanism of this protein?

An enzyme whose activity is controlled by allosteric regulation.

Explanation:

Enzymes are proteins that accelerate chemical reactions within the cell. Enzymes bind to the substrate in the active site, catalyzes the reaction, for example the breakdown of the binding molecule, and release the product or products.

The enzyme activity need to be regulated. One of the mechanisms by which this occurs involves effector molecules, usually small molecules which bind to the regulatory site, called allosteric site. The binding to effector molecules may activate or inhibit the enzyme activity, consequently increasing or decreasing the rate of the reaction.  

This mechanism of enzyme control is called allosteric regulation.

The description of the protein isolated fits with this features,  an enzyme whose activity is controlled by allosteric regulation.

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.