In: Biology
In active site of an enzyme, Valine and Alanine are NOT found.
The enzyme binds to its substrate at the active site of the enzyme which facilitates the conversion of substrate to product. The active site is a pocket which helps to fit the substrate.
The active sites contain amino acids that can be a part of catalytic cycle (His, Asp, Cys, Glu, Arg, Tyr, Lys) which enables proton and electron shuffling.
On the other hand, the amino acids which are less reactive are Trp, Thr, Gln, Phe along with amino acids with nonreactive side-chain (Met, Ala, Pro, Ile, Val, Leu) have low frequency of occurence in the active site.
Protein cores are rich in amino acids which are hydrophobic aliphatic (Ile, Leu, Val, Ala, Met) and aromatic amino acids (Phe, Trp). These amino acids help in maintaining the structural function for the stability of protein hydrophobic cores. On the other hand, the surface regions of the enzyme contain mainly charged (Lys, Arg, Glu, Asp) and polar residues (Asn, Gln), which facilitate contact with the polar water environment.