ESSENTIAL FATTY ACIDS (EFAs) Polyunsaturated FAs,such as Linoleic acid and g(gamma)- Linolenic acid, are ESSENTIAL FATTY ACIDS — we cannot make them, and we need them, so we must get them in our diets mostly from plant sources.

CLINICAL SIGNIFICANCE OF ENZYMES

The measurement of enzymes level in serum is applied in diagnostic application

Pancreatic Enzymes

Acute pancreatitis is an inflammatory process where auto digestion of gland was noticed with activation of the certain pancreatic enzymes. Enzymes which involves in pancreatic destruction includes α-amylase, lipase etc.,

1.  α-amylase (AMYs) are calcium dependent hydrolyase class  of metaloenzyme that catalyzes the hydrolysis of 1, 4- α-glycosidic linkages in polysaccharides. The normal values of amylase is in range of 28-100 U/L. Marked increase of 5 to 10 times the upper reference limit (URL) in AMYs activity indicates acute pancreatitis and severe glomerular impairment.

2.  Lipase is single chain glycoprotein. Bile salts and a cofactor called colipase are required for full catalytic activity of lipase. Colipase is secreted by pancreas. Increase in plasma lipase activity indicates acute pancreatitis and carcinoma of the pancreas.

Liver Enzymes

Markers of Hepatocellular Damage

1.  Aspartate transaminase (AST) Aspartate transaminase is present in high concentrations in cells of cardiac and skeletal muscle, liver, kidney and erythrocytes. Damage to any of these tissues may increase plasma AST levels.

The normal value of AST for male is <35 U/ L and for female it is <31 U/L.

2.  Alanine transaminase (ALT) Alanine transaminase is present at high concentrations in liver and to a lesser extent, in skeletal muscle, kidney and heart. Thus in case of liver damage increase in both AST and ALT were noticed. While in myocardial infarction AST is increased with little or no increase in ALT.

The normal value of ALT is <45 U/L and <34 U/L for male and female respectively

Markers of cholestasis

1.  Alkaline phosphatases

Alkaline phosphatases are a group of enzymes that hydrolyse organic phosphates at high pH. They are present in osteoblasts of bone, the cells of the hepatobiliary tract, intestinal wall, renal tubules and placenta.

Gamma-glutamyl-transferase (GGT) Gamma-glutamyl-transferase catalyzes the transfere of the γ–glutamyl group from peptides. The activity of GGT is higher in men than in women. In male the normal value of GGT activity is <55 U/L and for female it is <38 U/L.

2.  Glutamate dehydrogenase (GLD) Glutamate dehydrogenase is a mitochondrial enzyme found in liver, heart muscle and kidneys.

Muscle Enzymes

1.  Creatine Kinase Creatine kinase (CK) is most abundant in cells of brain, cardiac and skeletal.

2.  Lactate Dehydrogenase

Lactate dehydrogenase (LD) catalyses the reversible interconversion of lactate and pyruvate.

The input to fatty acid synthesis is acetyl-CoA, which is carboxylated to malonyl-CoA.

The ATP-dependent carboxylation provides energy input. The CO₂ is lost later during condensation with the growing fatty acid. The spontaneous decarboxylation drives the condensation. 

 fatty acid synthesis
acetyl-CoA + 7 malonyl-CoA + 14 NADPH → palmitate + 7 CO₂ + 14 NADP⁺ + 8 CoA

ATP-dependent synthesis of malonate:
8 acetyl-CoA + 14 NADPH + 7 ATP → palmitate + 14 NADP⁺ + 8 CoA + 7 ADP + 7 P_i

Fatty acid synthesis occurs in the cytosol. Acetyl-CoA generated in the mitochondria is transported to the cytosol via a shuttle mechanism involving citrate

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.

Glycolysis enzymes are located in the cytosol of cells.  Pyruvate enters the mitochondrion to be metabolized further

Mitochondrial compartments: The mitochondrial matrix contains Pyruvate Dehydrogenase and enzymes of Krebs Cycle, plus other pathways such as fatty acid oxidation. 

Pyruvate Dehydrogenase catalyzes oxidative decarboxylation of pyruvate, to form acetyl-CoA

FAD (Flavin Adenine Dinucleotide) is a derivative of the B-vitamin riboflavin (dimethylisoalloxazine-ribitol). The flavin ring system undergoes oxidation/reduction as shown below. Whereas NAD⁺ is a coenzyme that reversibly binds to enzymes, FAD is a prosthetic group, that is permanently part of the complex. 

FAD accepts and donates 2 electrons with 2 protons (2 H):

Thiamine pyrophosphate (TPP) is a derivative of  thiamine (vitamin B₁). Nutritional deficiency of thiamine leads to the disease beriberi. Beriberi affects especially the brain, because TPP is required for carbohydrate metabolism, and the brain depends on glucose metabolism for energy

Acetyl CoA, a product of the Pyruvate Dehydrogenase reaction, is a central compound in metabolism. The "high energy" thioester linkage makes it an excellent donor of the acetate moiety

For example, acetyl CoA functions as:

• input to the Krebs Cycle, where the acetate moiety is further degraded to CO₂.
• donor of acetate for synthesis of fatty acids, ketone bodies, and cholesterol.

ATPs  formed in TCA cycle from one molecule of Pyruvate

1. 3ATP            7. 3ATP          5. 3 ATP                     

 8. 1 ATP         9. 2 ATP          11.3 ATP         Total =15 ATP.

 ATPS formed from one molecule of Acetyl CoA =12ATP

ATPs formed from one molecule of glucose after complete oxidation

One molecule of glucose -->2 molecules of pyruvate

['By glycolysis] ->8 ATP

2 molecules of pyruvate [By TCA cycle] -> 30 ATP

Total = 38 ATP

Amino acids

Proteins are linear polymers of amino acids. Participate in virtually every biological process. Perform diverse functions:
       1. Enzymes: catalyze all reactions in living organisms
       2. Storage and transport
       3. Structural
       4. Mechanical work ( flagella, muscles, separation of chromosomes)
       5. Decoding information (translation, transcription, DNA replication)
       6. Cell-signalling (hormones and receptors)
       7. Defence (antibodies)