Question

Can any one do 2 and 3

Pyruvate kinase is one of the irreversible steps of glycolysis. The human genome has four genes that encode different pyruvate kinases, including a muscle specific form and a liver specific form. The liver specific form differs from the muscle specific form since it has additional regulation through phosphorylation by protein kinase A and allosteric regulation by the amino acid alanine. A V. vs. [S] plot of liver pyruvate kinase is shown below. hi 10 PKase activity (V.) F16BP none -Alanine - PKA nt [PEP] 1. What is the reaction catalyzed by pyruvate kinase? This is an example of substrate level phosphorylation. Define this term. (2 pts) 2. How does the hormone glucagon affect pyruvate kinase? Start with the binding of glucagon to the glucagon receptor and describe the sequence of events that leads to changes in pyruvate kinase activity (3 pts) 3. For the following. explain: 1. The influence on liver pyruvate kinase inhibitor or activator); II. The physiological rationale for regulation for each compound or regulator with respect to the cellular preference for gluconeogenesis or glycolysis. (4 pts) Fructose-1,6-bisphosphate Effect on activity: • Reason for regulation: Alanine Effect on activity: • Reason for regulation: Protein kinase A • Effect on activity: Reason for regulation: .

Answer 1

1. Pyruvate kinase catalyzes the transfer of a phoshate group from phoshoenol pyruvate (PEP) to adenosine diphoshate (ADP), yielding one molecule of pyruvate and one molecule of ATP. This is an example of substrate level phosphorylation. Substrate level phosphorylation is when ADP is converted to ATP by the direct transfer of a phosphate group. The phosphate group is transferred from a phosphorylate intermediate. It is a metabolic reaction that result in the formation of ATP or GTP by conversion of a higher energy substrate into lower energy product and a using some of released chemical energy.

2. Glucagon is a peptide hormone, produced by alphacells of pancreas. The pancreas releases glucagon when the amount of glucose in the blood stream is too low. Glucogon causes the liver to convert stored glycogen into glucose, whuch is released into the bloodstream.  

When glucogon binds to glucogon receptor, the liver cells convert the glycogen into individual glucose molecules and release them into the bloodstream, in a process known as glycogenesis. As these stores become depleted, glucagon then encourages the liver and kidney to synthesize additional glucose by gluconeogenesis.

3. Fructose 1, 6 bis phosphate as an intermediate present within the glycolytic pathway, FBP provides feed forward stimulation because the higher of concentration of FBP, the greater the allosteric activation and magnitude of pyruvate kinase activity. Pyruvate kinase is most sensitive to tge effect of FBP. The interconversion of fructose 1, 6-bisphoshate is stringently cintrolled. AMP stimulates phosphofructokinase, whereas ATP and citrate inhibit it.

The inhibition by alanine could be overcome by increasing tge conc of either phosphoenol pyruvate or fructose 1, 6-bisphoshate, although increasing the L-alanine concentration didnot appear to be able to reverse the activation by fructose1, 6- bisphoshate.

Pyruvate kinase activity is most broadly regulated by allosteric effectors, covalent modifiers and hormonal control. Pyruvate kinase has been activated by FBP and allosterically inactivated by ATP and alanine. Allosteric regulation is the binding of an effector to a site on the protein other than the active site, causing a cinformational change and altering the activity of that given protein or enzyme.

Protein kinase A is a family of enzymes whise activity is dependent on cellular level of cyclic AMP. Protein kinase A adds a phosphoryl grouos to glycogen synthase which leads to decrease in enzymatic activity.