Regulation, Vitamins, and Diagnostic Enzyme Function in Biochemistry

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 active site. This increases the apparent Km (substrate concentration at half-maximal velocity), but does not affect Vmax (maximum velocity).

• 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, permanently inactivating it.

Example: Sarin irreversibly inhibits acetylcholinesterase by covalent modification.

Enzyme Regulation

Mechanisms of Regulation

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

• Feedback Control: The end product of a pathway acts as an allosteric regulator for the first enzyme, either inhibiting (negative feedback) or enhancing (positive feedback) its activity.

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

Example: Phosphorylation of serine residues can activate or deactivate enzymes.

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.

Water-soluble vitamins are excreted in urine, while fat-soluble vitamins can accumulate and cause toxicity.

Fat-Soluble Vitamins

• Vitamin A (Retinol): Provitamin: β-carotene. Function: Vision, cell growth, antioxidant. Deficiency: Blindness, growth retardation. Toxicity: Liver damage.

• Vitamin D (Calciferol): Provitamin: 7-Dehydrocholesterol. Function: Bone growth, calcium absorption. Deficiency: Rickets. Toxicity: Calcification, kidney stones.

• Vitamin E (α-Tocopherol): Function: Antioxidant, prevents oxidative damage. Deficiency: Rare. Toxicity: Interferes with blood clotting.

• Vitamin K (Phylloquinone, Menaquinone): Function: Blood clotting, bone metabolism. Deficiency: Bleeding disorders. Toxicity: Liver dysfunction.

Water-Soluble Vitamins and Coenzymes

• Vitamin B1 (Thiamine): Coenzyme: Thiamine pyrophosphate (TPP). Function: Carbohydrate metabolism.

• Vitamin B2 (Riboflavin): Coenzymes: FMN, FAD. Function: Redox reactions.

• Vitamin B3 (Niacin): Coenzymes: NAD+, NADP+. Function: Redox reactions.

• Vitamin B5 (Pantothenic Acid): Coenzyme: Coenzyme A. Function: Acetyl group transfer.

• Vitamin B6 (Pyridoxine): Coenzyme: Pyridoxal phosphate (PLP). Function: Amino acid metabolism.

• Vitamin B7 (Biotin): Coenzyme: Biotin. Function: Carbon carrier in metabolism.

• Vitamin B9 (Folic Acid): Coenzyme: Tetrahydrofolate (THF). Function: Carrier of 1-carbon units.

• Vitamin B12 (Cobalamin): Coenzyme: Methylcobalamin. Function: Methyl transfer, nucleic acid metabolism.

• Vitamin C (Ascorbic Acid): Function: Antioxidant, collagen synthesis.

Diagnostic Enzymes and Serological Testing

Enzyme Markers for Disease Diagnosis

Specific enzymes in the blood can indicate organ damage or disease. For example, elevated levels of creatine kinase (CK), aspartate transaminase (AST), and lactate dehydrogenase (LDH) are used to diagnose heart attacks.

• CK (CPK): Heart attack marker.

• AST: Liver and heart damage marker.

• LDH: Red blood cell damage marker.

Lateral Flow Assay for COVID-19

Lateral flow assays are rapid diagnostic tests that use antibodies (a class of protective proteins) to detect antigens, such as the spike protein of SARS-CoV-2, in a sample.

• Antibodies: Bind specifically to target antigens.

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

Summary Tables

Water-Soluble Vitamins and Coenzymes

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	Functions
Vitamin A (retinol)	β-carotene	Vision, cell growth, antioxidant for lipids
Vitamin D (calciferol)	7-Dehydrocholesterol	Bone health, calcium and phosphate absorption
Vitamin E (α-tocopherol)	None	Antioxidant, prevents oxidative damage
Vitamin K (phylloquinone)	None	Blood clotting, bone metabolism

Additional info: These notes cover core concepts from Chapter 19 (Enzymes and Vitamins) and diagnostic enzyme function, directly relevant to GOB Chemistry topics such as enzyme regulation, inhibition, vitamin biochemistry, and serological testing.