Govt Exams
Km is the substrate concentration at which the reaction velocity is half of Vmax (V = Vmax/2), and it represents the affinity of enzyme for substrate. Lower Km indicates higher affinity.
The Lineweaver-Burk plot is a double reciprocal plot where 1/v is plotted against 1/[S], allowing easy determination of Km (x-intercept) and Vmax (y-intercept) from linear regression.
Chaperone proteins like HSP70 and HSP90 facilitate proper protein folding, prevent aggregation, and assist in maintaining protein stability, though some also work with degradation pathways.
Cooperative binding (positive cooperativity) occurs when binding of one substrate molecule enhances the affinity of the enzyme for additional substrate molecules, as seen in hemoglobin and phosphofructokinase.
Cytochrome c oxidase contains heme a, heme a3, and copper centers (CuA and CuB) essential for electron transfer and oxygen reduction.
Hyperammonemia type 1 (Reye's syndrome-like) results from CPS I deficiency, the first enzyme in the urea cycle. CPS I catalyzes ammonia fixation to form carbamoyl phosphate. Its deficiency prevents ammonia detoxification, causing neurotoxic accumulation.
In serine proteases like trypsin and chymotrypsin, histidine (His57) acts as a general acid-base catalyst. Its imidazole ring (pKa ~6) can both accept and donate protons, facilitating the nucleophilic attack by the serine hydroxyl group on the carbonyl carbon.
PDI catalyzes the formation, reduction, and rearrangement of disulfide bonds. In the oxidizing ER environment, PDI helps misfolded proteins achieve correct disulfide bonding patterns, acting as both an isomerase and a chaperone to prevent aggregation.
In zero-order kinetics (when substrate >> Km), all enzyme active sites are saturated. Velocity is directly proportional to enzyme concentration since V = kcat[E]total when enzyme is the limiting factor.
A Hill coefficient of 1.0 indicates no cooperativity and follows simple Michaelis-Menten kinetics. n > 1 indicates positive cooperativity (like hemoglobin), while n < 1 indicates negative cooperativity.