Glucagon

Glucagon, a peptide hormone synthesized and secreted from the α-cells of the islets of Langerhans of pancreas, raises blood glucose levels. The pancreas releases glucagon when blood sugar (glucose) levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is released into the bloodstream. Glucagon and insulin are part of a feedback system that keeps blood glucose levels at a stable level.

Regulation and function

Secretion of glucagon is stimulated by hypoglycemia, epinephrine, arginine, alanine, acetylcholine, and cholecystokinin.

Secretion of glucagon is inhibited by somatostatin, insulin, increased free fatty acids and keto acids into the blood, and increased urea production.

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

Vitamin B6: Pyridoxine, Pyridoxal, Pyridoxamine

Aids  in protein metabolism and red blood cell formation. It is also involved in the body’s production of chemicals such as insulin and hemoglobin.

Vitamin B6 Deficiency Deficiency symptoms include skin disorders, dermatitis, cracks at corners of mouth, anemia, kidney stones, and nausea. A vitamin B6 deficiency in infants can cause mental confusion.

Erythrocytes and the Pentose Phosphate Pathway

The predominant pathways of carbohydrate metabolism in the red blood cell (RBC) are glycolysis, the PPP and 2,3-bisphosphoglycerate (2,3-BPG) metabolism (refer to discussion of hemoglobin for review of the synthesis and role role of 2,3-BPG).

Glycolysis provides ATP for membrane ion pumps and NADH for re-oxidation of methemoglobin. The PPP supplies the RBC with NADPH to maintain the reduced state of glutathione.

The inability to maintain reduced glutathione in RBCs leads to increased accumulation of peroxides, predominantly H₂O₂, that in turn results in a weakening of the cell wall and concomitant hemolysis.

Accumulation of H₂O₂ also leads to increased rates of oxidation of hemoglobin to methemoglobin that also weakens the cell wall.

Glutathione removes peroxides via the action of glutathione peroxidase.

The PPP in erythrocytes is essentially the only pathway for these cells to produce NADPH.

Any defect in the production of NADPH could, therefore, have profound effects on erythrocyte survival.

Function of Calcium

The major functions of calcium are

(a) Excitation and contraction of muscle fibres needs calcium. The active transport system utilizing calcium binding protein is called Calsequestrin. Calcium decreases neuromuscular irritability.
(b) Calcium is necessary for transmission of nerve impulse from presynaptic to postsynaptic region.
(c) Calcium is used as second messenger in system involving protein and inositol triphosphate.
(d) Secretion of insulin, parathyroid hormone, calcium etc, from the cells requires calcium.
(e) Calcium decrease the passage of serum through capillaries thus, calcium is clinically used  to reduce allergic exudates.
(f) Calcium is also required for coagulation factors such as prothrombin.
(g) Calcium prolongs systole.
(h) Bone and teeth contains bulk quantity of calcium.

Enzymes are protein catalyst produced by a cell and responsible ‘for the high rate’ and specificity of one or more intracellular or extracellular biochemical reactions.

Enzymes are biological catalysts responsible for supporting almost all of the chemical reactions that maintain animal homeostasis. Enzyme reactions are always reversible.

The substance, upon which an enzyme acts, is called as substrate. Enzymes are involved in conversion of substrate into product.

Almost all enzymes are globular proteins consisting either of a single polypeptide or of two or more polypeptides held together (in quaternary structure) by non-covalent bonds. Enzymes do nothing but speed up the rates at which the equilibrium positions of reversible reactions are attained.

 In terms of thermodynamics, enzymes reduce the activation energies of reactions, enabling them to occur much more readily at low temperatures - essential for biological systems.