When is hexokinase active?

Last Update: May 30, 2022

This is a question our experts keep getting from time to time. Now, we have got the complete detailed explanation and answer for everyone, who is interested!

Asked by: Alexa Kling DVM
Score: 4.6/5 (49 votes)

Hexokinase undergoes an induced fit conformational change when glucose binds. This conformational change prevents the hydrolysis of ATP, and is allosterically inhibited by physiological concentrations of glucose-6-phosphate the product.

How is hexokinase activated?

Kinetics and Inhibition of Hexokinase

Hexokinase activates glycoloysis by phosphorylating glucose. ... Tissues where hexokinase is present use glucose at low blood serum levels. G6P inhibits hexokinase by binding to the N-terminal domain(this is simple feedback inhibition). It competitively inhibits the binding of ATP [8].

What activates hexokinase in glycolysis?

Hexokinase, the enzyme catalyzing the first step of glycolysis, is inhibited by its product, glucose 6-phosphate. ... In turn, the level of glucose 6-phosphate rises because it is in equilibrium with fructose 6-phosphate. Hence, the inhibition of phosphofructokinase leads to the inhibition of hexokinase.

What is the activity of hexokinase?

Hexokinase (HK), the red cell enzyme with the lowest activity in the glycolytic pathway, catalyzes the initial step in the utilization of glucose and thus is required for both glycolysis and the pentose shunt and produces glucose 6-phosphate.

Does insulin activate hexokinase?

Insulin has several effects in liver which stimulate glycogen synthesis. First, it activates the enzyme hexokinase, which phosphorylates glucose, trapping it within the cell.

Hexokinase: A VR Experience (2D version)

42 related questions found

Why is hexokinase not in the liver?

Liver contains an enzyme called glucokinase, which also carries out the [hexokinase] reaction, but is highly specific for D-glucose, has a much higher Km for glucose (approximately 10.0 mM ), and is not product-inhibited... ... It is weakly inhibited by glucose 6-phosphate (with an inhibition constant around 50 mM ).

What is the normal hexokinase?

When using the glucose oxidase and hexokinase methods, normal values are typically 70 to 99 mg/dl (3.9 to 5.5mmol/l). Medications, exercise, and recent illnesses can impact the results of the fasting blood sugar test, so an appropriate medical history should be taken before it is performed.

What is glucokinase and hexokinase?

Glucokinase and Hexokinase are enzymes which phosphorylate glucose to glucose-6-phosphate, trapping glucose inside the cell. Glucokinase is present in hepatocytes of the liver and beta cells of pancreas, tissues that needs to quickly respond to changes in glucose levels. ... Hexokinase is found in most tissues.

What happens if hexokinase is inhibited?

Whenever the concentration of glucose6-phosphate in the cell rises above its normal level, hexokinase is temporarily and reversibly inhibited, bringing the rate of glucose-6phosphate formation into balance with the rate of its utilization and reestablishing the steady state.

Is hexokinase in the liver?

Hexokinase is a family of four enzymes including glucokinase, also called hexokinase IV in liver and pancreatic islet cells.

What is the activator of hexokinase?

This effect of acidity is largely overcome by activators such as orthophosphate, citrate, malate, 3-phosphoglycerate, and riboside triphosphates. ... Thus, in the acid range, ATP appears to serve both as an activator and a substrate with the result that 1/v versus 1/[ATP] plots are nonlinear.

What does hexokinase bind to?

Hexokinase is the enzyme that catalyzes this phosphoryl-group-transfer. Hexokinase undergoes and induced-fit conformational change when it binds to glucose, which ultimately prevents the hydrolysis of ATP. It is also allosterically inhibited by physiological concentrations of its immediate product, glucose-6-phosphate.

What steps in glycolysis are irreversible?

3 irreversible steps in glycolysis: hexokinase; phosphofructokinase; pyruvate kinase. New enzymes are needed to catalyze new reactions in the opposite direction for gluconeogenesis.

How does hexokinase lower activation energy?

Hexokinase binds ATP only after glucose binds. This prevents the enzyme from catalyzing the reaction of ATP with water. ... This reduces the ability of the substrate to interact with the enzyme and the activation energy remains high.

Which hormone is responsible for Glycogenolysis?

Glucagon promotes glycogenolysis in liver cells, its primary target with respect to raising circulating glucose levels.

What type of enzyme is hexokinase?

A hexokinase is an enzyme that phosphorylates hexoses, which are sugars with six carbons, resulting in hexose phosphate. Glucoseis is the most important substrate of hexokinases in most organisms, while glucose-6-phosphate is the most important product.

What regulates hexokinase?

Hexokinase is the enzyme that catalyzes this phosphoryl group transfer. Hexokinase undergoes and induced-fit conformational change when it binds to glucose, which ultimately prevents the hydrolysis of ATP. It is also allosterically inhibited by physiological concentrations of its immediate product, glucose-6-phosphate.

Where is hexokinase III found?

HK3 is the predominant hexokinase in myeloid cells, particularly granulocytes.

What is glucokinase inhibited by?

Glucokinase is inhibited in the postabsorptive state by sequestration in the nucleus bound to GKRP, and it is activated postprandially by portal hyperglycemia and fructose through dissociation from GKRP, translocation to the cytoplasm, and binding to PFK2/FBP2.

Is glucokinase found in liver?

Glucokinase is one of four glucose phosphorylating enzymes present in rat liver. Its distinctive features are a high K-m for glucose (high-K-m isozyme) and a rather narrow substrate specificity.

How do hexokinase and glucokinase differ?

The main difference between hexokinase and glucokinase is that the hexokinase is an enzyme present in all cells whereas the glucokinase is an enzyme only present in the liver. Furthermore, hexokinase has a high affinity towards glucose while glucokinase has a low affinity towards glucose.

What is a glucokinase activator?

Glucokinase activators (GKAs) have been discovered recently that stimulate the enzyme allosterically by lowering its glucose S0.5 (the concentration of glucose that allows half-maximal activity of the enzyme) and Hill coefficient (nH) and increasing its catalytic constant (kcat).

Is 200 blood sugar normal after eating?

Less than 140 mg/dL (7.8 mmol/L) is normal. 140 to 199 mg/dL (7.8 mmol/L and 11.0 mmol/L) is diagnosed as prediabetes. 200 mg/dL (11.1 mmol/L) or higher after two hours suggests diabetes.