You Are Testing the Effects, on Insulin Function, to the Addition

You are testing the effects, on insulin function, to the addition of an unknown substance to adipocytes in culture. In the presence or absence of the compound you find that insulin binds to the adipocytes with equal affinity. Insulin alone results in a 5-fold increase in the rate of glucose uptake, above the basal rate. However, following addition of your test compound the rate of glucose uptake in response to insulin is only 0.5-fold above the basal rate. Your compound is actively taken up by the adipocytes and thus is likely exerting its effects intracellularly. Which of the following substances is your test compound most likely mimicking in this cell culture system?

A) ceramide
B) glucuronate
C) glucosamine
D) glucose
E) phosphatidic acid