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Phosphofructokinase (PFK) is an enzyme that plays a role in the breakdown of glycogen, a complex sugar that serves as a major energy source for the body. It is composed of four subunits, with different combinations of subunits found in various tissues. In skeletal muscles, PFK is solely composed of subunits produced from the PFKM gene, which provides instructions for creating the PFKM subunit. PFK is involved in the conversion of fructose-6-phosphate into fructose 1,6-bisphosphate, a key regulatory step in glycolysis, the process by which cells convert glucose into energy. This process is particularly important in skeletal muscles, which rely on glycolysis and aerobic respiration during exercise. Mutations in the PFKM gene can lead to conditions like glycogen storage disease type VII (GSDVII) or Tarui disease, characterised by muscle cramps, weakness, and myoglobinuria.
| Characteristics | Values |
|---|---|
| What is it? | An enzyme called phosphofructokinase (PFK) |
| What does it do? | Plays a role in the breakdown of a complex sugar called glycogen, which is a major source of stored energy in the body |
| What does it convert? | Fructose-6-phosphate to fructose-1,6-diphosphate or fructose 1,6-bisphosphate |
| What does it use? | ATP to phosphorylate fructose-6-phosphate |
| What is it composed of? | Four subunits, with different combinations of subunits found in different tissues |
| What is it associated with? | Caveolae and recruited to caveolae by caveolin-1 in VSMC |
| What does it regulate? | Glycolysis |
| What is it activated by? | Fructose-2,6-bisphosphate |
| What is it inhibited by? | ATP, PEP, citrate, and high levels of lactic acid |
| What is its role in cancer? | Cancer cells survive more effectively when they have a hyperactive phosphofructokinase 1 enzyme |
| What is its role in the body? | It is the main source of energy for cells |
| What happens when it is mutated? | It can cause Tarui disease, glycogen storage disease type VII (GSDVII), or muscle weakness and cramping |
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What You'll Learn
- The PFKM gene provides instructions for making the PFKM subunit of the phosphofructokinase enzyme
- Phosphofructokinase deficiency can cause Tarui disease, a glycogen storage disease
- Phosphofructokinase is involved in the breakdown of glycogen to provide energy to muscle cells
- The enzyme is composed of four subunits, with different combinations found in different tissues
- Phosphofructokinase is a key regulatory step of glycolysis, catalysing the conversion of fructose-6-phosphate into fructose 1,6-bisphosphate
The PFKM gene provides instructions for making the PFKM subunit of the phosphofructokinase enzyme
The phosphofructokinase enzyme is composed of four subunits, with different combinations of subunits found in various tissues. In skeletal muscles, which are responsible for movement, the enzyme is made up solely of subunits produced from the PFKM gene. This muscle-specific isozyme is one of three types, along with liver and platelet isozymes, that function as subunits of the mammalian tetramer phosphofructokinase.
The PFKM subunit plays a crucial role in the regulation of glycolysis. It catalyses the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, which is a key regulatory step in the glycolytic pathway. This reaction is ATP-dependent, and phosphofructokinase can be allosterically inhibited by high levels of ATP, preventing unnecessary ATP production through glycolysis. Additionally, PFKM is allosterically activated by ADP, AMP, or fructose 2,6-bisphosphate, allowing the cell to adjust the rate of glycolysis based on its energy needs.
Mutations in the PFKM gene can disrupt the function of the PFKM subunit, leading to a condition known as glycogen storage disease type VII (GSDVII) or Tarui disease. This disease is characterised by an inability to break down glycogen in muscle cells, resulting in muscle cramps, weakness, and in some cases, muscle destruction. The severity of symptoms can vary among affected individuals, and certain mutations are more commonly associated with specific populations, such as those with Ashkenazi Jewish ancestry.
In summary, the PFKM gene plays a vital role in energy production by providing instructions for the synthesis of the PFKM subunit of the phosphofructokinase enzyme. This subunit is essential for the breakdown of glycogen and the regulation of glycolysis, particularly in skeletal muscles. Mutations in the PFKM gene can lead to GSDVII, emphasising the critical role of this gene in maintaining muscle function and overall energy homeostasis in the body.
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Phosphofructokinase deficiency can cause Tarui disease, a glycogen storage disease
Phosphofructokinase (PFK) is an enzyme that plays a role in the breakdown of glycogen, a complex sugar and a major source of stored energy in the body. It is made up of four subunits, with different combinations of subunits found in different tissues. In skeletal muscles, the phosphofructokinase enzyme is composed solely of subunits produced from the PFKM gene.
PFK catalyses the ATP-dependent phosphorylation to convert fructose-6-phosphate into fructose 1,6-bisphosphate and ADP. It is a key regulatory step of glycolysis, which is the process by which cells convert glucose into energy.
PFK deficiency is a rare muscular metabolic disorder characterised by a deficiency in the PFK enzyme throughout the body, including the skeletal muscles and red blood cells. It is an autosomal recessive disorder, meaning that both parents must be carriers of the genetic defect for their child to be born with the disease. The PFKM gene mutation results in the production of PFKM subunits that have little to no function. This leads to a decrease in overall PFK enzyme function, impairing the ability of cells to use carbohydrates for energy.
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Phosphofructokinase is involved in the breakdown of glycogen to provide energy to muscle cells
Phosphofructokinase (PFK) is an enzyme that plays a role in the breakdown of glycogen, a complex sugar and a major source of stored energy in the body. The phosphofructokinase enzyme is made up of four subunits and is found in a variety of tissues. In skeletal muscles, the enzyme is composed solely of subunits produced from the PFKM gene.
PFK is involved in the breakdown of glycogen to provide energy to muscle cells. This process is particularly important when energy is needed, such as during exercise or to maintain normal blood glucose levels between meals. During exercise, skeletal muscles activate glycolysis and consume glucose, using both aerobic and anaerobic respiration.
PFK catalyses the ATP-dependent phosphorylation to convert fructose-6-phosphate into fructose 1,6-bisphosphate and ADP. This is a key regulatory step of glycolysis, as PFK can regulate glycolysis through allosteric inhibition. The cell can thus increase or decrease the rate of glycolysis in response to its energy requirements. For example, a high ratio of ATP to ADP will inhibit PFK and glycolysis.
PFK is also involved in the breakdown of glycogen in other ways. For instance, serotonin (5-HT) increases PFK by binding to the 5-HT(2A) receptor, causing the tyrosine residue of PFK to be phosphorylated via phospholipase C. This, in turn, redistributes PFK within the skeletal muscle cells.
Mutations in the PFKM gene can cause glycogen storage disease type VII (GSDVII), resulting in an inability to break down glycogen in muscle cells. This can lead to muscle cramps and weakness that can vary in severity.
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The enzyme is composed of four subunits, with different combinations found in different tissues
The phosphofructokinase enzyme is made up of four subunits, with different combinations of subunits found in different tissues. The PFKM gene provides instructions for making one piece (the PFKM subunit) of the phosphofructokinase enzyme. This enzyme plays a role in the breakdown of a complex sugar called glycogen, which is a major source of stored energy in the body.
In muscles used for movement (skeletal muscles), the phosphofructokinase enzyme is composed solely of subunits produced from the PFKM gene. The cells' main source of energy is stored as glycogen. When energy is required, glycogen can be rapidly broken down into the simple sugar glucose. Phosphofructokinase, composed of PFKM subunits, is involved in the sequence of events that breaks down glycogen to provide energy to muscle cells.
In other tissues, other subunits that make up the phosphofructokinase enzyme likely compensate for the lack of PFKM subunits, and the enzyme is able to retain some function. This compensation may explain why other tissues are not affected by PFKM gene mutations. Mutations in the PFKM gene can cause glycogen storage disease type VII (GSDVII), characterised by an inability to break down glycogen in muscle cells, resulting in muscle cramps and weakness.
Phosphofructokinase (PFK) is a regulatory enzyme of glycolysis, catalysing the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate. PFK is allosterically inhibited by high levels of ATP, but AMP reverses this inhibitory action. Thus, the activity of the enzyme increases when the cellular ATP/AMP ratio is lowered, stimulating glycolysis when energy levels fall.
PFK also has a role in cancer, with cancer cells requiring a hyperactive phosphofructokinase 1 enzyme to meet their energy requirements for rapid cell growth and division.
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Phosphofructokinase is a key regulatory step of glycolysis, catalysing the conversion of fructose-6-phosphate into fructose 1,6-bisphosphate
Phosphofructokinase (PFK) is a crucial enzyme in the breakdown of glycogen, a complex sugar that serves as a significant energy reserve in the body. PFK specifically catalyses the conversion of fructose-6-phosphate into fructose 1,6-bisphosphate, a key regulatory step in glycolysis. This process is essential for maintaining energy homeostasis in the body, particularly in skeletal muscles, where PFK plays a vital role in energy production during exercise or other physical activities.
PFK exists in two isoforms: PFK-1 and PFK-2. While PFK-1 catalyses the conversion of fructose-6-phosphate into fructose 1,6-bisphosphate, PFK-2 is responsible for converting fructose 6-phosphate into fructose 2,6-bisphosphate. This distinction is important as these two isoforms have different regulatory functions in glycolysis and other metabolic pathways.
PFK-1 is a critical regulator of the glycolytic pathway, controlling the rate-limiting step of converting fructose-6-phosphate to fructose 1,6-bisphosphate. This step is irreversible and sets the pace for the entire glycolytic process. The activity of PFK-1 is influenced by various factors, including ATP, ADP, AMP, citrate, and magnesium (Mg2+) concentrations, as well as the presence of specific allosteric activators and inhibitors.
One of the key regulators of PFK-1 is fructose 2,6-bisphosphate, which is produced from fructose-6-phosphate by PFK-2. Fructose 2,6-bisphosphate acts as a potent allosteric activator of PFK-1, increasing its affinity for fructose-6-phosphate and enhancing the glycolytic flux. This activation is particularly important in muscle cells, where it helps prevent the accumulation of excess acid, protecting the muscles from damage during exercise or other strenuous activities.
PFK also plays a significant role in various clinical conditions, such as glycogen storage diseases and cancer. Mutations in the PFKM gene, which encodes the muscle isoform of PFK, can lead to glycogen storage disease type VII (GSDVII), characterised by muscle cramps and weakness due to the impaired breakdown of glycogen in muscle cells. On the other hand, cancer cells, with their high energy demands, often exhibit increased activity of PFK to meet their rapid cell growth and division requirements.
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Frequently asked questions
Muscle phosphofructokinase is an enzyme that plays a role in the breakdown of glycogen, a complex sugar and major source of stored energy in the body.
Muscle phosphofructokinase converts fructose-6-phosphate to fructose-1,6-bisphosphate, a process known as phosphorylation. This process is a key regulatory step of glycolysis, which is the basis of both anaerobic and aerobic respiration.
The PFKM gene provides instructions for making the PFKM subunit of the muscle phosphofructokinase enzyme. The PFKM subunit is found in muscle, heart, brain, and testis tissue.
Mutations in the PFKM gene can cause glycogen storage disease type VII (GSDVII), a condition characterised by an inability to break down glycogen in muscle cells. This results in muscle cramps and weakness.
Phosphofructokinase-1 (PFK-1) is a form of phosphofructokinase that catalyses the rate-limiting step of glycolysis. It is highly regulated to respond to the changing energy needs of the cell.
