Short Notes on PLP Coenzymes and TPP
i) PLP Coenzymes (Pyridoxal Phosphate)
Introduction
Pyridoxal phosphate (PLP) is the active coenzyme form of vitamin B6. It is essential for the metabolism of amino acids and is involved in various biochemical reactions as a coenzyme.
Structure and Source
- PLP is derived from vitamin B6 (pyridoxine).
- It contains a reactive aldehyde group that forms Schiff base intermediates with amino acids.
Functions
- Acts as a coenzyme in transamination, decarboxylation, and racemization of amino acids.
- Plays a crucial role in neurotransmitter synthesis, such as serotonin and dopamine.
- Involved in glycogen breakdown by activating glycogen phosphorylase.
Mechanism
PLP forms a covalent bond with the amino group of the substrate, facilitating the transformation into different products depending on the reaction type.
Clinical Relevance
- Deficiency can lead to neurological symptoms, including irritability and depression.
- PLP levels are important in managing conditions like epilepsy and carpal tunnel syndrome.
ii) TPP (Thiamine Pyrophosphate)
Introduction
TPP is the active coenzyme form of vitamin B1 (thiamine). It is involved in carbohydrate metabolism and is essential for energy production.
Structure and Source
- TPP is synthesized from thiamine and contains a thiazolium ring crucial for its activity.
- Found in whole grains, nuts, and legumes.
Functions
- Acts as a coenzyme for enzymes involved in oxidative decarboxylation of alpha-keto acids, such as pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase.
- Essential in the pentose phosphate pathway via transketolase enzyme.
Mechanism
The thiazolium ring in TPP stabilizes carbanion intermediates during decarboxylation, enabling smooth progression of the reaction.
Clinical Relevance
- Deficiency causes beriberi and Wernicke-Korsakoff syndrome, particularly in alcoholics.
- Vital for proper functioning of the nervous system and heart.
Conclusion
Both PLP and TPP are critical coenzymes derived from B-vitamins, playing significant roles in amino acid and carbohydrate metabolism respectively. Their importance in enzymatic reactions highlights the necessity of vitamins in sustaining life and metabolic balance.