Sphingosine-1-phosphate (SIP) Is important for cell survival. The synthesis of S

Question

Sphingosine-1-phosphate (SIP) Is important for cell survival. The synthesis of SIP from sphingosine and ATP is catalyzed by the enzyme sphingosine kinase. An understanding of the kinetics of the sphingosine kinase reaction may be Important in the development of drugs to treat cancer. The velocity of the sphingosine kinase reaction was measured in the presence and absence of three-sphingosine, a stereoisomer of sphingosine that inhibits the enzyme. The results are shown below. Construct a Lineweaver-Burk plot to answer the following questions. What are the apparent Km and Vmax values in the absence of the inhibitor (considered correct If within 5% of the value)? What are the apparent Km and Vmax values in the presence of the inhibitor (considered correct if within 5% of the value)? What kind of an inhibitor is three-sphingosine?

Explanation / Answer

V= VmaxS/(KM+S), 1/V= (KM/Vmax)*1/S + 1/Vmax

Lineweaver- burk plot is given by 1/V vs 1/S. The slope is KM/Vmax and intercept is 1/Vmax

for the case of no inhibition, 1/Vmax= 0.010, Vmax= 100 mg/min

KM/Vmax= 0.051, KM= 0.051*100 =5.1 uM

for the case of inhibition, Vmax= 100 mg/min and KM/Vmax= 0.271, Km=0.271*100 =27.1 uM

Since Vmax is same for both the cases, it is competitive inhibition.

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