Regulation, Vitamins, and Their Significance to Enzyme Function; Serological Testing

Enzyme Inhibition

Types of Enzyme Inhibition

Enzyme inhibition is a critical concept in biochemistry, describing how molecules can decrease or halt enzyme activity. There are several types of inhibition, each affecting enzyme function differently.

• Competitive Inhibition: The inhibitor resembles the substrate and competes for the same binding site on the enzyme. This type of inhibition increases the apparent Km (decreases affinity) but does not affect Vmax.

• Noncompetitive Inhibition: The inhibitor binds to a site other than the active site, causing a conformational change that prevents substrate binding. Vmax is decreased, but Km remains unchanged.

• Uncompetitive Inhibition: The inhibitor binds only to the enzyme-substrate complex, not to the free enzyme. Both Km and Vmax are decreased by the same ratio.

• Irreversible Inhibition: The inhibitor covalently modifies the enzyme, rendering it permanently inactive.

Example: Sarin irreversibly inhibits acetylcholinesterase by covalent modification.

Enzyme Regulation

Mechanisms of Regulation

Enzymes in metabolic pathways are regulated to ensure proper cellular function and energy efficiency. Regulation can be achieved through several mechanisms:

• Feedback Control: The end product of a pathway acts as an allosteric regulator for an enzyme early in the pathway. Negative feedback inhibits the enzyme, while positive feedback enhances its activity.

• Allosteric Regulation: Molecules bind to sites other than the active site, causing conformational changes that affect enzyme activity. Positive regulators increase activity; negative regulators decrease it.

• Covalent Modification: Addition or removal of functional groups (e.g., phosphorylation) alters enzyme activity.

• Zymogen Activation: Enzymes are synthesized in inactive forms (proenzymes) and activated by removal of a protein segment.

• Genetic Control: Regulation of enzyme levels through gene expression.

Vitamins and Coenzymes

Classification of Vitamins

Vitamins are essential organic molecules required for various biological functions. They are classified based on their solubility:

• Water-Soluble Vitamins: Hydrophilic, contain OH and COOH groups, not stored in the body, often form coenzymes. Examples: Vitamin C, B-complex vitamins.

• Fat-Soluble Vitamins: Hydrophobic, mainly composed of carbon and hydrogen, stored in the liver. Examples: Vitamins A, D, E, K.

Reason for Classification: Solubility affects storage, absorption, and toxicity. Water-soluble vitamins are excreted easily, while fat-soluble vitamins can accumulate and cause toxicity.

Biological Functions and Sources of Vitamins

Each vitamin has a specific biological function and source. Some are ingested as provitamins and converted to active forms in the body.

Vitamin	Alternate Name	Provitamin	Function	Source
A	Retinol	β-carotene	Vision, cell growth, antioxidant	Carrots, dairy, liver
D	Calciferol	7-Dehydrocholesterol	Bone health, Ca2+ absorption	Sunlight, fish, milk
E	α-tocopherol	None	Antioxidant	Nuts, seeds, oils
K	Phylloquinone	None	Blood clotting	Leafy greens

Coenzymes Derived from Vitamins

Coenzymes are organic compounds required for enzyme catalysis. Many water-soluble vitamins are precursors to coenzymes.

Vitamin	Coenzyme	Function
B1 (Thiamine)	Thiamine pyrophosphate (TPP)	Decarboxylation
B2 (Riboflavin)	FAD, FMN	Electron transfer
B3 (Niacin)	NAD+, NADP+	Oxidation-reduction
B5 (Pantothenic acid)	Coenzyme A	Acetyl group transfer
B6 (Pyridoxine)	Pyridoxal phosphate (PLP)	Transamination
B7 (Biotin)	Biocytin	Carboxylation
B9 (Folic acid)	Tetrahydrofolate (THF)	Methyl group transfer
B12 (Cobalamin)	Methylcobalamin	Methyl transfer
C (Ascorbic acid)	Vitamin C	Collagen synthesis, antioxidant

Diagnostic Enzymes and Serological Testing

Enzyme-Based Diagnostics

Enzyme activity in blood can be used to diagnose organ damage or disease. Specific enzymes are associated with particular organs.

• Heart Attack: Elevated levels of Creatine Kinase (CK), Aspartate Transaminase (AST), and Lactate Dehydrogenase (LDH) indicate myocardial infarction.

• Liver Dysfunction: Alanine Transaminase (ALT), γ-Glutamyl transferase (GGT), and Alkaline Phosphatase (ALP) are markers for liver health.

• Pancreas: α-Amylase is used to assess pancreatic function.

• Prostate: Prostate Specific Antigen (PSA) is used for prostate health screening.

Serological Testing: Lateral Flow Assay

Lateral flow assays are rapid diagnostic tests used to detect antigens, such as the COVID-19 spike protein. These tests use protective proteins (antibodies) to bind specific targets.

• Principle: Antibodies on the test strip bind to the target antigen, producing a visible signal.

• Procedure: Sample is applied, flows through the strip, and results are read visually.

Summary Tables

Water-Soluble Vitamins

Vitamin	Coenzyme	Function
Thiamine (B1)	Thiamine pyrophosphate	Decarboxylation
Riboflavin (B2)	FAD, FMN	Electron transfer
Niacin (B3)	NAD+, NADP+	Oxidation-reduction
Pantothenic acid (B5)	Coenzyme A	Acetyl group transfer
Pyridoxine (B6)	Pyridoxal phosphate	Transamination
Cobalamin (B12)	Methylcobalamin	Methyl group transfer
Ascorbic acid (C)	Vitamin C	Collagen synthesis, healing
Biotin	Biocytin	Carboxylation
Folic acid	Tetrahydrofolate	Methyl group transfer

Fat-Soluble Vitamins

Vitamin	Provitamin	Function
A (retinol)	β-carotene	Vision, cell growth, antioxidant
D (calciferol)	7-Dehydrocholesterol	Bone health, Ca2+ absorption
E (α-tocopherol)	None	Antioxidant
K (phylloquinone)	None	Blood clotting