Question

Glucokinase A. has a Sos greater than the normal blood glucose concentration. B. is found in muscle. C. is inhibited by glucose 6 -phosphate. D. is also known as the GLUT-2 protcin. E has glucose 6 -phosphatase activity as well as kinase activity.

Short answer

A. Glucokinase has a Sos greater than the normal blood glucose concentration. B. Glucokinase is found in muscle. C. Glucokinase is inhibited by glucose 6-phosphate. D. Glucokinase is also known as the GLUT-2 protein. E. Glucokinase has glucose 6-phosphatase activity as well as kinase activity. Answer: A

Step-by-step solution

Understanding Glucokinase

Glucokinase is an enzyme found in the liver and some other cells, which catalyzes the transfer of a phosphate group from adenosine triphosphate (ATP) to glucose, producing glucose 6-phosphate (G6P) as a product. The main function of glucokinase is to help maintain glucose homeostasis by initiating a series of reactions in the glycolysis pathway and the glycogen synthesis pathway.

Evaluate Statement A

Statement A claims that glucokinase has a Sos (substrate concentration at which the reaction rate is half the maximum reaction rate) greater than the normal blood glucose concentration. This statement is true, as glucokinase has a high Km (which correlates with Sos), meaning that the enzyme's activity is relatively low at normal blood glucose concentrations. This property allows glucokinase to act as a glucose sensor and be primarily active when blood glucose levels are elevated.

Evaluate Statement B

Statement B claims that glucokinase is found in muscle. This statement is false. Glucokinase is not present in muscles; instead, muscles contain a similar enzyme called hexokinase, which differs in substrate specificity and regulatory properties.

Evaluate Statement C

Statement C claims that glucokinase is inhibited by glucose 6-phosphate (G6P). Although G6P is an allosteric inhibitor of hexokinase, this statement is false, as glucokinase is not inhibited by G6P. This is important in the liver, as glucose metabolism can continue even when the concentrations of G6P are high.

Evaluate Statement D

Statement D claims that glucokinase is also known as the GLUT-2 protein. This statement is false. Glucokinase and GLUT-2 are distinct proteins with different functions. Glucokinase is an enzyme involved in glucose phosphorylation, whereas GLUT-2 is a glucose transporter responsible for transporting glucose across the plasma membrane of various cells.

Evaluate Statement E

Statement E claims that glucokinase has glucose 6-phosphatase activity as well as kinase activity. This statement is false. Glucokinase only catalyzes the phosphorylation of glucose to form G6P and does not have glucose 6-phosphatase activity. Glucose 6-phosphatase is a separate enzyme found primarily in the liver, which catalyzes the dephosphorylation of G6P to glucose, enabling the release of glucose into the bloodstream.