Regulation of enzyme activity Flashcards
What are IC50 values? What do they tell us about the relative effectiveness of inhibitors?
IC50 values tell us the concentration of an inhibitor that is needed to half the activity of the enzyme inhibited. The lower the value of IC50, the more effective the inhibitor.
What are the roles of metal ions as cofactors?
- Redox reagents e.g. iron ions in cytochrome p450s
- part of the active site and involved in electrostatic substrate binding e.g. magnesium ions in kinases and zinc ions in carbonic anhydrase
- Regulate the activity of the enzyme e.g. calcium ions in proteases
What are coenzymes? Give examples
Coenzymes are organic molecules. Many water-soluble vitamins are coenzymes are apart of coenzymes. Many coenzymes carry reaction components e.g. NADH and FADH2 carry electrons which act as reducing power. Coenzyme A carries acyl groups, the smallest being acetyl groups. Thiamine pyrophosphate and Biotin carry CO2 units for biosynthesis. A severe deficiency in Vitamin C causes scurvy. A deficiency in niacin - or tryptophan (a precursor of NAD) produces pellagra. This presents as dementia, diaherrha and dermatitis.
How is Glucose-6-Phosphate used in the body?
Some is used in glycolysis to release energy. Others is used in the Pentose-phosphate pathway to result in the synthesis of nucleic acid and produce NADP+
What is Glucose-6-Phosphate dehydrogenase deficiency? What is the effect of this deficiency.
X-linked recessive disorder. Most carriers are asymptomatic as the pentose phosphate pathway is not the only source of NADP+. When symptomatic, the disorder can lead to a haemolytic crisis when exposed to certain drugs or foods. A an infant this deficiency can lead to brain damage or jaundice.
What is Primaquine induced haemolytic anaemia?
Primaquine is an old anti-malerial. NADPH is needed to make glutathione. Glutathione repairs oxidatively damaged lipid membranes. In the reduced form glutathione can rescue the the oxidatively damaged lipid membranes; then it becomes oxidised and needs to be recycled. Glutathione reductase keeps the Glutathione in its reduced state and to do this utilises NADPH. Primaquine stimulates reactive oxygen species, damaging a lot of lipid membranes and so uses up a lot of NADPH. If they do not have the enzyme (G6PDH), they cannot make any more NADPH. This leads to haemolytic anaemia as RBC only make NADPH through glucose-6-phosphate and so lipid damage increases and the RBC is at risk.
What is Favism?
Favism is a disease that results from a deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD). Favism usually is due to a genetic disorder, but also can result from consumption of broad beans resulting in haemolytic anaemia.
How is enzyme activity controlled?
- Using activation through proteolysis for example and covalent modification (e.g. phosphorylation through kinase enzymes. Phosphate groups are removed using phosphatases)
- Through feedback regulations
- Inhibitions through natural or pharmaceutical inhibitors.
What is the role of series proteases? How are the activity of these proteins controlled?
Serine proteases are enzymes that cleave peptide bonds in proteins, in which serine serves as the nucleophilic amino acid at the (enzyme’s) active site. These can activate other enzymes. The action of these enzymes are controlled using endogenous inhibitors and feedback regulation. Examples of these inhibitors include antithrombin - switches of the blood clotting cascade - and antitrypsin.
What is proteolysis?
Inactive zymogen (proenzyme) is activated by proteases. This is an irreversible activation of an enzyme after removal of part of a peptide chain. For example Trypsin and chymotrypsin are made in the pancreas but activated once in the duodenum. Trypsin and Chymotrypsin both self-activate at some point in the cascade. In Chymotrypsin bonds are cleaved, the peptides remain together due to disulphide bridges, In other cases, some peptides are cleaved off. Trypsinogen (the zymogen to trypsin) is activated to trypsin as a small extension chain is cleaved off. Trypsin can then go and activate other proteins such as elastase and chymotrypsin.
How are serpins involved in the blood clotting cascade?
Tissue-type plasminogen activator (TPA) - a serpin, activates plasminogen to produced plasmin. plasmin can then catalysis the reaction to break down fibrin to produce soluble peptides. This can be used in treatment as a ‘clot buster’ and can highly improve the chances of a thrombosis sufferer.
