Question

Please help! And show your work/explain reasoning

A pH vs. kcat study was done on HCBR and the resulting plot is found below. What is the likely amino that is responsible for the the observed pH dependency and in which type of catalysis is it most likely participating? Explain your reasoning for your answers to both parts of this question. Use the O_2 binding curves to the left to address the following: a. If the proximal histidine were mutated to an alanine for each of the hemoglobin subunits, would curve 1 or curve 4 most likely result? Briefly explain. b. Curves 3 and 4 were measured in this presence of 10 mM or 20 mM 2, 3-bisphosphoglycerate. Which of the two curves was taken done in the presence of 10 mM 2, 3-bisphosphoglycerate? Briefly explain.

Answer 1

(a) The amino acid might be glutamicacid (b) it is general acid catalysis because the rate is higher at low pH(more acidic) condition. with increase in pH, rate also decreased. (2) curve '4' is more likely result. The binding of 'O_2' to iron centre results in the conformational change in histamine residue towards the porphyry in in the structure of hemoglobin molecule which results in an increased 'O_2' affinity of hemoglobin. if his tidied is replaced with almandine, the affinity to 'O_2' will decrease, so curve '4' might be the result. (3) curve '3': More 'O_2' affinity than that in curve '4'in presence of 2, 3 - BPG, O_2 is less tightly bound to hemoglobin. So at higher concentration of 2, 3 - BPG, less affinity to 'O_2' 10mM less concentration so curve '3' 20mM more concentration so curve '4'