Monday's Molecule #168

This molecule is present in most (all?) species. Your mission for today, should you choose to accept it,¹ is to: (a) name this molecule, (b) identify the most important enzyme that uses it as a substrate, and (c) name an important competitive inhibitor of this enzyme.

Post your answer in the comments. I'll hold off releasing any comments for 24 hours. The first one with the correct answers wins. I will only post mostly correct answers to avoid embarrassment. The winner will be treated to a free lunch.

There could be two winners. If the first correct answer isn't from an undergraduate student then I'll select a second winner from those undergraduates who post the correct answer. You will need to identify yourself as an undergraduate in order to win. (Put "undergraduate" at the bottom of your comment.)

Some past winners are from distant lands so their chances of taking up my offer of a free lunch are slim. (That's why I can afford to do this!)

In order to win you must post your correct name. Anonymous and pseudoanonymous commenters can't win the free lunch.

Winners will have to contact me by email to arrange a lunch date.

Comments are invisible for 24 hours. Comments are now open.

UPDATE: The molecule is HMG-CoA or 3-hydroxy-3-methylglutaryl Coenzyme A. The enzyme is HMG-CoA reductase, a key enzyme in the pathway leading to synthesis of cholesterol. Competitive inhibitors of this enzyme are used to reduce blood cholesterol levels by blocking synthesis of endogenous cholesterol. The most common inhibitors are the statins such as atorvastin (Lipitor) and lovastatin (Mevacor). The winner is undergraduate Sean Ridout.

Winners
Nov. 2009: Jason Oakley, Alex Ling
Oct. 17: Bill Chaney, Roger Fan
Oct. 24: DK
Oct. 31: Joseph C. Somody
Nov. 7: Jason Oakley
Nov. 15: Thomas Ferraro, Vipulan Vigneswaran
Nov. 21: Vipulan Vigneswaran (honorary mention to Raul A. Félix de Sousa)
Nov. 28: Philip Rodger
Dec. 5: 凌嘉誠 (Alex Ling)
Dec. 12: Bill Chaney
Dec. 19: Joseph C. Somody
Jan. 9: Dima Klenchin
Jan. 23: David Schuller
Jan. 30: Peter Monaghan
Feb. 7: Thomas Ferraro, Charles Motraghi
Feb. 13: Joseph C. Somody
March 5: Albi Celaj
March 12: Bill Chaney, Raul A. Félix de Sousa
March 19: no winner
March 26: John Runnels, Raul A. Félix de Sousa
April 2: Sean Ridout
April 9: no winner
April 16: Raul A. Félix de Sousa
April 23: Dima Klenchin, Deena Allan
April 30: Sean Ridout

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1. I watched Mission: Impossible - Ghost Protocol on a recent flight from San Diego to Toronto. You should only do this when you've exhausted all other options.