How Does Rennin Affect The Rate Of Enzyme Activity

Enzymes are catalytic proteins that selectively speed up chemical reactions without by consumed by the reaction itself (1). Enzyme activity is significantly affected by factors such as temperature, substrate concentration, enzyme concentration and pH. Enzymes are highly specific and only catalyse one specific chemical reaction, speeding up the reaction by lowering the activation energy, the energy required to start a chemical reaction (2). At high temperatures and with various mechanical forces or chemical treatments, proteins can denature causing it to lose its conformational features and hence its ability to function.
The enzyme examined in this experiment, rennin, is derived from the stomachs of calves, lambs or goats before consumption of anything but milk. Rennin is initially secreted as an inactive proenzyme called prochymosin, which is activated
upon exposure to acids such as HCl and converted into the active enzyme rennin (3). However, rennin can also be sourced commercially as junket tablets which are used as an industrial catalyst in cheese and dessert making. Enzyme consists of a sequence of single peptide chains containing 323 amino acid residues. (4)
Rennin is a protein digesting enzyme which causes its substrate caseinogen (5), commonly found in milk, to form a curd, forming insoluble casein, allowing the liquids to separate and run off as whey.
Rennin catalyses the conversion of the protein of milk, caseinogen, into paracasein, which is precipitated as a calcium salt. (6)
Rennin requires specific conditions to function, thriving at temperatures between 29°C-40°C, with an optimal temperature of 37 °C. Above 37°C, rennin molecules increase in energy causing the rate of reaction to increase, becoming denatured at approximately 60°C. Below 37°C, the reduced energy level results in fewer collisions and the rate of reaction and activity of rennin decreases. (7)
The optimum pH for rennin is pH 3.4 (8) as it mimics the gastric juices and acidic conditions of the stomach, however again rennin functions well between ph5 and pH7 actively attacking casein and coagulating milk. Rennin has maximum stability at pH 5.4 and begins to denature above pH 7. It is also affected by substrate concentration; the higher the concentration of calcium ions, the faster the rate of
reaction.
The aim of this experiment was to measure the effect of temperature on rennin activity by observing the rate of coagulation of milk. As rennin is known to catalyst the conversion of milk proteins, the rate of coagulation i.e. time it takes for milk to clot, holds a direct correlation to enzyme activity and function. Our hypothesis is that rennin will coagulate fastest at 37°C because it is the optimal temperature for rennin function, thus resulting in a faster rate of reaction. We further predict that above 37°C but below 60°C, enzyme activity will be slower and above 60°C and below 20°C, the enzyme should cease to function.