Carefully read the passage and sel ectthe best response to a question. Calculati
ID: 267227 • Letter: C
Question
Carefully read the passage and sel ectthe best response to a question. Calculations may be required. . Hexokinase (HK) catalyzes the transfer of the terminal phosphate from ATP to glucose to from glucose-6- phosphate and ADP. A tropical disease researcher has isolated the HK produced by the pathogenic protozoan known as Trypanosoma brucei, the causative agent of African sleeping sickness. The viability of this organism requires a functional HK. After being considered an important target for drug development, research began to develop a novel hexokinase kinase inhibitor via screening a library of 256,000 compounds. The most effective compound, HK-1990-001, reduced the Vmax of the trypanosome HK by 50% at a concentration of 0.5 ??. HK-1990-001 had no significant effect on Km. Other experiments indicate that inhibition is reduced when [ATPl is increased at constant [Glucose] and [HK-1990-001] is 1.0 ??. Inhibition is not reduced when [Glucose] is increased at constant ATP) and [HK-1990-001] is 1.0 ??. Since humans also require functional HK, experiments were performed to determine if HK-1990-001 inhibited human HK. The results of those "control" experiments revealed that Vmax for the human enzyme decreased by 50% at a [HK-1990-001-50.0 M. At 50 M inhibitor, Km increased approximately 1 0.5%. Like the trypanosome enzyme, inhibition was reduced when [ATP] is increased at constant [Glucose] and [HK-1990-001] is 10.0 ??. inhibition was not reduced when [Glucose] is increased at constant [ATP] and [HK-1990-001] is 10.0 ?? For comparison, the kinetic parameters obtained when assays were performed at 1 HM enzyme in the absence of HK-1 are provided in the table Km (uM) Glucose Km (uM) ATP Vmax (uM/min) 1000 500 200 100 200 500 Human rypanosoma Based on the information in this passage select the best answer(s) to each question 1. The enzyme described above is best classified as a exhibiting what type of kinetic fingerprint? A) Ping-pong B) Random C)Ordered D) Allosteric 2. Compared to the human enzyme, the catalytic rate constant for the trypanosomal enzyme is A) Equal B) 2.5-fold greaterC 2.5-fold less D) Cannot determine 3. The kinetic behavior of both enzymes in the presence of HK-1 is indicative of C) noncompetitive inhibition A) competitive inhibition D) irreversible inhibition B) uncompetitive inhibitionExplanation / Answer
The given enzyme has allosteric type of kinetic fingerprinting. 2.5 fold less. Competitive inhibition.