Usually, an enzyme molecule has only one active site, and the active site fits with one specific type of substrate. An active site contains a binding site that binds the substrate and orients it for catalysis. Residues in the binding site form hydrogen bonds, hydrophobic interactions, or temporary covalent interactions (van der Waals) with the substrate to make an enzyme-substrate complex.
The decreased volume only disrupts the equilibrium if the moles of gaseous products and moles of gaseous reactants are unequal. If there are an equal number of moles of gaseous substances on both sides of the arrow, the change in volume has an equal effect on the concentrations of reactants and of products.
Reason density decreases at temperatures above 4Â°C are the same as for any other material - thermal expansion. Reason that density decreases at temperatures bellow 4Â°C is a bit more complicated. Ice has lower density than water because the ice crystal is fairly sparse. There is a lot of empty space within the crystal structure. At temperatures well above freezing, water molecules move individually.