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Vitamins and coenzymes, and their significance in metabolism

Dr. Kavisa Ghosh, Assistant Professor, Department of Biotechnology, The Oxford College of Science,

Bengaluru, Karnataka 560102, India.

Abstract

Vitamins are not all biosynthesised in the body. Humans can synthesise Vitamin B3 (niacin) and Vitamin D

but primarily acquire the other essential vitamins from their diet. Deficiency in vitamins can lead to various

disorders or diseases. Enzymes cannot work independently on their own. They require cofactors (minerals)

and coenzymes that make them catalytically active. Many of these coenzymes are derived from vitamins.

Additionally, coenzymes play a crucial role in catabolic and anabolic pathways. This review provides in- depth detail about vitamins, their biological function, types of coenzymes and their significance in

metabolism.

Keywords: Vitamins, enzymes, coenzymes and metabolism

1.0 Introduction

Vitamins are chemical compounds that are necessary for homeostasis in the body, and their absence leads to

various diseases [1]. Vitamins do not provide direct energy but act as coenzymes and aid in the process of

metabolism. Enzymes are biomolecules made up of protein that help in the metabolic reactions in the body.

Enzymes cannot work independently, they require cofactors (minerals) and coenzymes, which make them

catalytically active. Many of these coenzymes are derived from vitamins [2]. Coenzymes play a very crucial

role in both catabolic and anabolic pathways [3].

1.1 Vitamins and their role in the biological system

Vitamins are widely classified as fat soluble (A, D, E and K) and water soluble (B complex and vitamin C).

Not all vitamins function as coenzymes. A, C, D, E, and K vitamins have a diverse array of functions.

Vitamin A, also known as retinol, is the precursor for the production of retinal, which is a light-sensitive

group present in rhodopsin and other visual pigments. Vitamin A also aids in the production of retinoic acid

that serves as an important signalling molecule in the body. Deficiency of vitamin A leads to the occurrence

of night blindness. Vitamin C, also known as ascorbate, acts as an antioxidant in the body and protects the

body from free radicals by neutralising them. Deficiency in vitamin C can cause scurvy, a disease

characterised by the malformed collagen accompanied with distinct skin lesions and fragile blood-vessels.

One of the metabolites of vitamin D acts as a hormone (1,25-dihydroxycholecalciferol) that help regulate the

metabolism of calcium and phosphorus in the body. Deficiency in vitamin D leads to impairment of bone

formation in the body and causes rickets in children and osteomalacia in adults. vitamin E, also known as α- tocopherol, protects the mitochondrial machineries from inactivation. Vitamin E reacts with reactive oxygen

species (ROS) such as the hydroxyl radicals (•OH) and neutralizes them before ROS can oxidize the

unsaturated lipids in membrane and damage cellular components. Vitamin K is required for the formation of

vitamin K dependent blood clotting factors for normal blood clotting formation. Fat soluble vitamins can be

stored in the body (liver and fat tissues), however excess intake can lead to toxic conditions such as

hypervitaminoses. Water soluble vitamins are required on a daily basis through our diet for proper

functioning of the body. Water soluble enzymes are involved in the formation of coenzymes and aid in

Science, Technology and Development

Volume XI Issue IV APRIL 2022

ISSN : 0950-0707

Page No : 461

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various metabolic reactions. The role of vitamin C as a coenzyme is unknown. The types of vitamin B and

their respective deficiency consequences are listed in Table 1.1. [4, 5].

Table 1.1. Types of vitamin B and respective deficiency consequences. (Adapted from: Berg et al., 2012

[4]).

Vitamin Consequences of deficiency

Thiamine (B1) Beriberi (weight loss, heart problems, neurological

dysfunction)

Riboflavin (B2) Cheliosis and angular stomatitis (lesions of the mouth),

dermatitis

Pyridoxine (B6) Depression, confusion, convulsions

Nicotinic acid (niacin) (B3) Pellagra (dermatitis, depression, diarrhea)

Patothenic acid Hypertension

Biotin (B7) Rash about the eyebrows, muscle pain, fatigue(rare)

Folic acid (folate) Anemia, neural-tube defects in development

Cobalamin (B12) Anemia, pernicious anemia, methylmalonic acidosis

1.2 Coenzymes

There coenzymes can be divided into two types, one that are not derived from vitamins and the other that are

derived from vitamins. Coenzymes can also be called as carrier molecules that are required for metabolism.

The coenzymes that are not derived from vitamins include: ATP, lipoamide, s-adenosylmethionine, uridine

diphosphate glucose, cytidine diphosphate diacylglycerol, and nucleotide triphosphates. Most of the

coenzymes required for metabolism are derived from vitamins. The function and coenzyme from vitamins

are listed in Table 1.2.

Table 1.2.Vitamins, their coenzyme forms and processes promoted. (Adapted from: McKee and McKee,

2004 [5]).

Vitamin Coenzyme form Reaction or process promoted

Water-soluble vitamins

Thiamine (B1) Thiamine pyrophosphate Decarboxylation, aldehyde group

transfer

Riboflavin (B2) FAD and FMN Redox

Pyridoxine (B6) Pyridoxal phosphate Amino group transfer

Nicotinic acid (niacin) NAD and NADP Redox

Patothenic acid Coenzyme A Acyl transfer

Biotin Biocytin Carboxylation

Folic acid Tetrahydrofolic acid One-carbon group transfer

Vitamin B12 Deoxyadenosylcobalamin,

methylcobalamin

Intramolecular rearrangements

Ascorbic acid (Vitamin C) Unknown Hydroxylation

Lipid-soluble vitamins

Vitamin A Retinal Vision, growth, and reproduction

Vitamin D 1-25-

Dihydroxycholecalciferol

Calcium and phosphate

metabolism

Vitamin E Unknown Lipid antioxidant

Vitamin K Unknown Blood clotting

Science, Technology and Development

Volume XI Issue IV APRIL 2022

ISSN : 0950-0707

Page No : 462