The cytochrome P450 constitute a superfamily of heme-containing enzymes that occur in nearly all living organisms, from bacteria to mammals, These monooxygenases, which in animals are embedded in the endoplasmic reticulum membrane, catalyze reactions of the sort

                  RH + O₂ + 2 H⁺ + 2e⁻ → ROH + H₂O 

The electrons (e−) are supplied by NADPH, which passes them to cytochrome P450’s heme prosthetic group via the intermediacy of the enzyme NADPH P450 reductase. Here RH represents a wide variety of usually lipophilic compounds for which the different cytochromes P450 are specific. They include

a. polycyclic aromatic hydrocarbons 

b. polycyclic biphenyls

c. frequently carcinogenic compounds that are present in tobacco smoke, broiled meats, and other pyrolysis products

d. which were widely used in electrical insulators and as plasticizers and are also carcinogenic.

#Question id: 558

#Unit 1. Molecules and their Interaction Relevant to Biology

In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the:

#Question id: 559

#Unit 1. Molecules and their Interaction Relevant to Biology

In competitive inhibition, an inhibitor:

#Question id: 560

#Unit 1. Molecules and their Interaction Relevant to Biology

Vmax for an enzyme-catalyzed reaction:

#Question id: 561

#Unit 1. Molecules and their Interaction Relevant to Biology

Enzyme X exhibits maximum activity at pH = 6.9.  X shows a fairly sharp decrease in its activity when the pH goes much lower than 6.4.  One likely interpretation of this pH activity is that:

#Question id: 562

#Unit 1. Molecules and their Interaction Relevant to Biology

Phenyl-methane-sulfonyl-fluoride (PMSF) inactivates serine proteases by binding covalently to the catalytic serine residue at the active site; this enzyme-inhibitor bond is not cleaved by the enzyme.  This is an example of what kind of inhibition?

#Question id: 563

#Unit 1. Molecules and their Interaction Relevant to Biology

Both water and glucose share an —OH that can serve as a substrate for a reaction with the terminal phosphate of ATP catalyzed by hexokinase.  Glucose, however, is about a million times more reactive as a substrate than water.  The best explanation is that: