BIOCHEMISTRY - Main Regulators and Biological Fluids of the Human Body - 2016

1. ENZYMES

1.2. Structure and Properties of Enzymes

Enzymes have a high molecular weight ranging from 10,000 to 1,000,000 Daltons and exhibit all the physical and Chemical properties of Proteins.

Both simple (proteins) and complex (protein conjugates/holoenzymes) enzymes exist in nature. Thus, based on their Structure, enzymes are divided into two groups: proteins and Conjugated Proteins.

Simple proteins consist solely of a protein molecule (e.g., enzymes such as Pepsin, Trypsin, urease, Lysozyme, and phosphatase).

Most natural enzymes are conjugated proteins (protein conjugates). They consist of a protein moiety, known as the apoenzyme, and a non-protein active component, known as the coenzyme (coenzyme, cofactor, prosthetic group). A coenzyme can be a small-molecule substance of either inorganic or organic origin (vitamin derivatives, NUCLEOTIDES, Metal Ions, etc.).

Coenzymes represent the Active Site of the enzyme and perform diverse Functions. They can act either as carriers of various functional groups or as enzyme activators. For instance, vitamin B₆ as part of the Pyridoxal phosphate enzyme catalyzes the Transamination of Amino acids (The transfer of an amino group), NAD transfers electrons and hydrogen, coenzyme A (CoA) transfers acyl groups, and so on.

Sometimes coenzymes are tightly bound to the apoenzyme—linked to the polypeptide chain via covalent bonds; such coenzymes are referred to as prosthetic groups.

There are two distinct centers within The structure of an enzyme protein molecule.

1. The active site, which serves to bind the enzyme to the substrate. This is a specific region of the enzyme molecule shaped like a cleft or a depression. It determines the Specificity and catalytic activity of the enzyme.

2. The allosteric site, which serves as the binding place for activators (which increase enzyme activity) or inhibitors (which decrease enzyme activity).

Any alteration in the enzyme's structure disrupts the active or allosteric site, resulting in the loss of enzymatic activity.

About one-third of all known enzymes contain a metal ion or are activated by metal ions. The strength of the bond between the metal and the protein moiety varies widely. Some enzymes lose their metal ion during isolation due to dissociation, whereas others retain it during purification; these are known as metalloenzymes (Metalloproteins).