Enzymes

Most enzymes found intracellularly, althougt some are normally found in plasma (e.g., coagulation factors)
Enzymes may appear in serum due to tissue damage or from degraded cells
Enzyme sites:
- Active site (where substrate interacts)
- Allosteric site (non-active site, where regularly molecules may bind)
Parts of Enzyme:
- Holoenzyme: complete, active enzyme
- Apoenzyme: protein portion of the enzyme, which requires a cofactor for increased activity (or any activity at all)
- Co-factor: non-portion portion that transiently binds to the enzyme to enhance the apoenzyme's ability to catalyze a reaction
  - Co-enzymes: organic co-factors that are loosely bound to act as intermediate carriers of electrons, etc.
    - Vitamin B
    - NAD, NADP, NADH
  - Prosthetic groups: organic co-factors that are permanently bound to apoenzyme and undergo chemical changes during the reaction
    - Heme
  - Metal ions: inorganic ions that activate enzymatic reactions
    - Zn2+, Mg2+, Fe2+, occasionally anions like Cl

Factors Affecting Enzymes

pH (optimal pH for maximal activity)
temperature (increased temperature increases enzyme activity until it is denatured)
co-factors
inhibitors

Proenzymes (Zymogens)

Inactive enzyme or precursor that is activated by an activator
- Digestive enzymes inactive to protect tissue when not required

Isoenzymes

Functionally identical (same active centre), but the enzyme itself is different physically (e.g., different amino acid side chains)
Identified by different chemical properties
Creatine kinase
Lactate dehydrogenase

Enzyme Specificity

Reaction Kinetics

1st Order Reaction
- Reaction rate increases in proportion to the amount of substrate added
Zero Order Reaction