During severe liver damage, an enzyme (E1 of problem A) is released into the blo

Question

During severe liver damage, an enzyme (E1 of problem A) is released into the bloodstream. After severe exercise, a muscle enzyme, E3, that catalyzes the same reaction is released into the blood stream. E1 and E3 can be differentiated easily because they have different Km values. (The Km of the muscle enzyme is 2 X 10-5 M.) An assay of a blood sample of a patient gave the results given below. Is the patient suffering from blood disease, or has he simply been exercising strenuously? The patient arrived at the hospital unconscious, so you can’t ask him any questions.

  [S] (M)                       v (moles/ml serum/min)

5.0 X 10-5                    43                                           

7.0 X 10-5                    57                                           

1.0 X 10-4                    75                                           

1.5 X 10-4                    100                                         

2 X 10-4                       120                                         

3 X 10-4                       150                                         

6 X 10-4                       200

Explanation / Answer

Some biological reactions in the absence of enzymes may be as much as a million times slower. Virtually all enzymes are proteins, though the converse is not true and other molecules such as RNA can also catalyze reactions. The most remarkable characteristics of enzymes are their ability to accelerate chemical reactions and their specificity for a particular substrate. Enzymes take advantage of the full range of intermolecular forces (van der waals interactions, polar interactions, hydrophobic interactions and hydrogen bonding) to bring substrates together in most optimal orientation so that reaction will occur. Also, enzymes can be inhibited by specific molecules by called competitive, uncompetitive, and noncompetitive inhibitors.

Catalysis happens at the active site of the enzyme. It contains the residues that directly participate in the making and breaking of bonds. These residues are called the catalytic groups. Although enzymes differ widely in structure, specificity, and mode of catalysis a number of generalizations concerning their active sites can be made:

1. The active site is a three dimensional cleft or crevice formed by groups that come from different parts of the amino acid sequence - residues far apart in the amino acid sequence may interact more strongly than adjacent residues in the sequence.

2. The active site takes up a relatively small part of the total volume of an enzyme. Most of the amino acid residues in an enzyme are not in contact with the substrate, which raises the question of why enzymes are so big. Nearly all enzymes are made up of more than 100 amino acid residues. The "extra" amino acids serve as a scaffold to create the three dimensional active site from the amino acids that are far apart in the primary structure. In many proteins the remaining amino acids also constitute regulatory sites, sites of interaction with other proteins, or channels to bring the substrate to the active sites.

3. Active sites are unique microenvironments. In all enzymes of known structure, substrate molecules are bound to a cleft or crevice. Water is usually excluded unless it is a reactant. The nonpolar microenvironment of the cleft enhances the binding of substrates as well as catalysis. Nevertheless, the cleft may also contain polar residues. Certain of these polar residues acquire special properties essential for substrate binding or catalyis.

4. Substrates are bound to enzymes by multiple weak interactions.

Related Questions

Navigate

• Browse (All)
• Browse D
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.