CLASSIFICATION OF ENZYMES

1. Oxidoreductases : Act on many chemical groupings to add or remove hydrogen atoms. e.g. Lactate dehydrogenase

2. Transferases Transfer functional groups between donor and acceptor molecules. Kinases are specialized transferases that regulate metabolism by transferring phosphate from ATP to other molecules. e.g. Aminotransferase.

3. Hydrolases Add water across a bond, hydrolyzing it. E.g. Acetyl choline esterase

4. Lyases Add water, ammonia or carbon dioxide across double bonds, or remove these elements to produce double bonds. e.g. Aldolase.

5. Isomerases Carry out many kinds of isomerization: L to D isomerizations, mutase reactions (shifts of chemical groups) and others. e.g. Triose phosphate isomerase

6. Ligases Catalyze reactions in which two chemical groups are joined (or ligated) with the use of energy from ATP. e.g. Acetyl CoA carboxylase

CALCIUM

Total calcium in the human body is 1 to 1.5kg, out of which 99% is seen in bone and 1% in extracellular fluid. The main source of calcium is milk.

The daily requirement of calcium for child is 1200mg/day and for adult it is 500mg/day. During pregnancy /lactation the calcium requirement is 1500mg/day.

The absorption of calcium takes place in 1st and 2nd part of deuodenum. Calcium absorption requires carrier protein, helped by Ca²⁺ - dependent ATpase.

Factors responsible for increase in calcium absorption include Vitamin D, Parathyroid hormone, acidity and amino acids. Factors such as phytic acid,oxalates, malabsorption  syndromes and Phosphates decreases calcium absorption. The normal calcium level in blood is 9-11mg/dl.

Glycogenolysis

Breakdown of  glycogen to glucose is called glycogenolysis. The Breakdown of glycogen takes place in liver and muscle. In Liver , the end product of glycodgen breakdown is glucose where as in muscles the end product is Lactic acid Under the combined action of Phosphorylase  (breaks only –α-(1,4) linkage )and Debranching enzymes (breaks only α-(1,6) linkage )glycogen is broken down to glucose.

ZINC

The enzyme RNA polymerase, which is required for transcription, contains zinc and it is essential for protein bio synthesis.

Deficiency in Zinc leads to poor wound healing, lesions of skin impaired spermatogenesis, hyperkeratosis, dermatitis and alopecia

 Ketogenic Only

 Mnemonic: "LL is Keto" (Leucine, Lysine)

Glucogenic Only

Both Ketogenic & Glucogenic

Mnemonic: "I Prefer To Try Tasty Yogurt" (I, Phe, T, Trp, Tyr)

The Effects of Enzyme Inhibitors

Enzymes can be inhibited

• competitively, when the substrate and inhibitor compete for binding to the same active site or
• noncompetitively, when the inhibitor binds somewhere else on the enzyme molecule reducing its efficiency.

The distinction can be determined by plotting enzyme activity with and without the inhibitor present.

Competitive Inhibition

In the presence of a competitive inhibitor, it takes a higher substrate concentration to achieve the same velocities that were reached in its absence. So while V_max can still be reached if sufficient substrate is available, one-half V_max requires a higher [S] than before and thus K_m is larger.

Noncompetitive Inhibition

With noncompetitive inhibition, enzyme molecules that have been bound by the inhibitor are taken out

• enzyme rate (velocity) is reduced for all values of [S], including
• V_max and one-half V_max but
• K_m remains unchanged because the active site of those enzyme molecules that have not been inhibited is unchanged.