Write the action of:

HIGH Ca2+ ON PTH:

High extracellular Ca2+ level would allow Ca2+ to interact with acidic residues of extracellular domain of seven spanning membrane G protein coupled receptors. Binding of Ca2+ to receptor results in conformational change in receptor such that coupling to G-protein results in  lowered cAMP levels and decreased PTH secretion. High Ca2+ level may cause a person to feel run down, cause to sleep poorly, make them more irritable than usual, and even cause a disease in memory.

AROMATASE ON TESTOSTERONE:

Aromatase belongs to cytochrome P450 family. During aromatization reactions, aromatase forms an electron transfer complex with NADPH cytochrome P450 reductase. This enzyme converts androstenedione to estrogen and testosterone to estradiol by aromatizing androgens. Factors that increase the activity of aromatase include age, obesity, insulin gonadotrophins, alcohol and smoking.

CHOLERA TOXIN ON G-PROTEIN:

Cholera toxin activates cAMP production. The A subunit of the toxin activates the heterotrimeric G-protein, GS-alpha, via ADP ribosylation. The modified GS-alpha loses its GTPase activity but remains constitutively active in its GTP bound state, causing a continuous stimulation of adenylate cyclase. It leads to excessive cAMP production. The result is secretion of chloride ions from the cell.

DEIODINASE ON MIT AND DIT:

TG tyrosyl residues are iodinated to form MIT and DIT which on subsequent oxidative coupling forms iodothyronines i.e., T3 and T4. MIT, DIT along with T3 and T4 are transported into the cell in the form of colloid droplets. These droplets fuse with lysosome to form secondary lysosome. The iodinated tyrosine i.e., MIT and DIT are released into cytosol through lysosomal proteolysis which is then deiodinated by deiodinase enzyme and the iodide formed is recycled for use within the cell.

HYPOXIA ON ERYTHROPOIETIN:

Hypoxia is a state of low oxygen tension in tissues. Erythropoietin counteract tissue hypoxia by increasing systemic oxygen carrying capacity. It induces augmentation of red blood cells mass by stimulating the formation and differentiation of erythroid precursor cells in bone marrow. An oxygen sensor that controls hypoxia induced erythropoietin synthesis is located in kidney. Changes in oxygen flux may be detected by tubular epithelial cells and transmitted to adjacent peritubular endothelial cells, resulting in induction of gene for EP. Several signaling molecules such as transcription factor Hypoxia-inducible factor 1 (HIF-1) are involved in EP transcriptional response to cellular hypoxia.

L-AROMATIC AMINO ACID DECARBOXYLASE ON DOPA.

L-Aromatic Amino acid decarboxylase (AAAD) is an essential enzyme for the formation of catecholamines, indolamines and trace amines. It is a non-specific decarboxylase found in many tissues and helps in converting L-DOPA to dopamine by the decarboxylation of L-DOPA. This enzyme is important when treating patients with Parkinson's disease.

3-beta HYDROXY STEROID DEHYDROGENASE AND delta 5,4 ISOMERASE ON DEHYDROEPIANDROSTERONE:

3-beta hydroxy steroid dehydrogenase and delta-5,4 isomerase acts on dehydroandrosterone i.e., a 17- hydroxysteroid and is converted by side chain cleavage to androstenedione i.e., 17-ketosteroid. This androstenedione is further converted into testosterone which regulates male reproductive behavior.