FACTORS AFFECTING ENZYME ACTIVITY

Velocity or rate of enzymatic reaction is assessed by the rate of change in concentration of substrate or product at a given time duration. Various factors which affect the activity of enzymes include:

1. Substrate concentration

2. Enzyme concentration

3. Product concentration

4. Temperature 5. Hydrogen ion concentration (pH)

6. Presence of activators

7. Presence of inhibitor

Effect of substrate Concentration :  Reaction velocity of an enzymatic process increases with constant enzyme concentration and increase in substrate concentration.

Effect of enzyme Concentration: As there is optimal substrate concentration, rate of an enzymatic reaction or velocity (V) is directly proportional to the enzyme concentration.

Effect of product concentration In case of a reversible reaction catalyzed by a enzyme, as per the law of mass action the rate of reaction is slowed down with equilibrium. So, rate of reaction is slowed, stopped or even reversed with increase in product concentration

Effect of temperature: Velocity of enzymatic reaction increases with temperature of the medium which they are most efficient and the same is termed as optimum temperature.

Effect of pH: Many enzymes are most efficient in the region of pH 6-7, which is the pH of the cell. Outside this range, enzyme activity drops off very rapidly. Reduction in efficiency caused by changes in the pH is due to changes in the degree of ionization of the substrate and enzyme.

Highly acidic or alkaline conditions bring about a denaturation and subsequent loss of enzymatic activity

Exceptions such as pepsin (with optimum pH 1-2), alkaline phosphatase (with optimum pH 9-10) and acid phosphatase (with optimum pH 4-5)

Presence of activators Presence of certain inorganic ions increases the activity of enzymes. The best examples are chloride ions activated salivary amylase and calcium activated lipases.

Effect of Inhibitors The catalytic enzymatic reaction may be inhibited by substances which prevent the formation of a normal enzyme-substrate complex. The level of inhibition then depends entirely upon the relative concentrations of the true substrate and the inhibitor

HORMONES

A hormone is a chemical that acts as a messenger transmitting a signal from one cell to another. When it binds to another cell which is the target of the message, the hormone can alter several aspects of cell function, including cell growth, metabolism, or other function.

Hormones can be classified on three primary ways as following:

1.  Autocrine: An autocrine hormone is one that acts on the same cell that released it.

2.  Paracrine: A paracrine hormone is one that acts on cells which are nearby relative to the cell which released it. An example of paracrine hormones includes growth factors, which are proteins that stimulate cellular proliferation and differentiation.

3. Endocrine: An endocrine hormone is one that is released into the bloodstream by endocrine glands. The receptor cells are distant from the source. An example of an endocrine hormone is insulin, which is released by the pancreas into the bloodstream where it regulates glucose uptake by liver and muscle cells.

Role of Coenzymes

The functional role of coenzymes is to act as transporters of chemical groups from one reactant to another.

Ex. The hydride ion (H+ + 2e-) carried by NAD or the mole of hydrogen carried by FAD;

The amine (-NH2) carried by pyridoxal phosphate

Polyprotic Acids

• Some acids are polyprotic acids; they can lose more than one proton.

• In this case, the conjugate base is also a weak acid.

• For example: Carbonic acid (H2CO3 ) can lose two protons sequentially.

• Each dissociation has a unique Ka and pKa value.

Ka₁ = [H+ ][HCO₃ ^- ] / [H₂CO₃]

Ka₂ = [H+ ][CO₃ ^-2 ] / [HCO₃^- ] 

Note: (The difference between a weak acid and its conjugate base differ is one hydrogen)

Gluconeogenesis

It is the process by which Glucose or glycogen is formed from non carbohydrate substances.

Gluconeogenesis occurs mainly in liver.

Gluconeogenesis inputs:  
The source of pyruvate and oxaloacetate for gluconeogenesis during fasting or carbohydrate starvation is mainly amino acid catabolism. Some amino acids are catabolized to pyruvate, oxaloacetate, Muscle proteins may break down to supply amino acids. These are transported to liver where they are deaminated and converted to gluconeogenesis inputs. 
Glycerol, derived from hydrolysis of triacylglycerols in fat cells, is also a significant input to gluconeogenesis

Glycolysis & Gluconeogenesis pathways are both spontaneous If both pathways were simultaneously active within a cell it would constitute a "futile cycle" that would waste energy

Glycolysis yields 2~P bonds of ATP.
Gluconeogenesis expends 6~P  bonds of ATP and GTP.
A futile cycle consisting of both pathways would waste 4 P.bonds per cycle.To prevent this waste, Glycolysis and Gluconeogenesis pathways are reciprocally regulated.

Pantothenic Acid

Pantothenic Acid is involved in energy production, and aids in the formation of hormones and the metabolism of fats, proteins, and carbohydrates from food.

RDA The Adequate Intake (AI) for Pantothenic Acid is 5 mg/day for both adult males and females.

Pantothenic Acid Deficiency

Pantothenic Acid deficiency is uncommon due to its wide availability in most foods.