Question

1. Explain enzyme kinetics, regulation and its use as a diagnostic marker.

Answer 1

Enzymes are proteins that function as biological catalysts responsible for supporting almost all the chemical reactions that keep animal homeostasis. So their assay and pharmacological regulation have become , key elements in clinical diagnosis and therapeutics.

They are found in all tissues and fluids of the body. Intracellular enzymes catalyze the reactions of metabolic pathways.Plasma membrane enzymes regulate the catalysis within cells in response to extracellular signals. So every significant life process is dependent in enzyme activity.

Enzymes regenerate during the reaction that catalyze. They act by speeding up the reaction rate without affecting the equilibrium constant of the reaction.

This effect is the consequence of the decrease in the amount of energy required to form a complex of substrates to produce products : activated or transient state. So the free energy required is much lower, allowing that in one instant a greater proportion of substrates molecules can achieve this activated state, resulting in an increasing of reaction rate.

In all this process, enzymes recognize specifically the substrate of the reaction that catalyze, binds to it and form a transient complex E-S that advanced to E-Product complex. Finally, free enzyme is liberated from product molecules.This step sequence takes place following a characteristic kinetic.

All reactions enzymatically catalyzed, can reach a max speed  rate according to enzyme concentration or substrate availability

The study of kinetic properties is useful in the design and clinical use of drugs that selectively can alter rate constants interfering in the progress of disease states

But enzyme activity is also naturally regulated by the action of activators or inhibitors that binds to the enzyme, inducing conformational or affinity changes that can affect the action rate.

Inhibitors can act in different ways : by reversible or irreversible processes; and inhibiting by competitive or non competitive way.

But, in the cells , enzymes are part of multistep metabolic pathways, so their activity is linked to the activity of other enzymes of the same pathway.The enzymatic activity in this case, can be regulated at different points:

- genetic level: modulation of level of expression of genes that encode enzymes

- protein level: proteolysis or covalent modifications

- allosteric enzymes: are regulated by the binding of effector molecules that induce conformational changes , altering the enzyme activity ( many PK are regulated by cAMP)

Diagnostic markers use

The measurement of enzymes in plasma have diagnostic significance because indicates that tissue or cellular damage is taking place , releasing intracellular components into the blood.

ie:

Liver enzymes : marker of hepatic damage

Cardiac troponins: myocardial infarct

Creatine kinase: marker muscle or brain damage

Lactate dehydrogenase: marker of myocardial infarction