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: 1124

#SCPH28 | Zoology

Which of the following is (are) intracellular second messengers?

a. Ca2+                        b. cAMP          c. epinephrine             

d. protein kinase A      e. protein kinase C

#Question id: 1125

#SCPH01 Biochemistry

Examples of G protein–coupled receptors include

a. rhodopsin receptor.             b. β-adrenergic receptor.

c. insulin receptor.                   d. acetylcholine receptor.

#Question id: 1125

#SCPH28 | Zoology

Examples of G protein–coupled receptors include

a. rhodopsin receptor.             b. β-adrenergic receptor.

c. insulin receptor.                   d. acetylcholine receptor.

#Question id: 1126

#SCPH01 Biochemistry

Which of the following statement(s) is (are) true of the α subunit of a G protein?

a. It physically associates with the receptor.              

b. It binds GDP.

c. It binds GTP.                     

d. It is a transmembrane protein.

#Question id: 1126

#SCPH28 | Zoology

Which of the following statement(s) is (are) true of the α subunit of a G protein?

a. It physically associates with the receptor.              

b. It binds GDP.

c. It binds GTP.                     

d. It is a transmembrane protein.

#Question id: 1127

#SCPH01 Biochemistry

Which of the following steps does not occur after acetylcholine binds to the muscarinic acetylcholine receptor in heart muscle cells?