ENZYMES & METABOLISM
Casey G. Turner, RN
Biochemistry
Western Governors University
ENZYMES
• Enzymes act as catalysts and speed up reactions
• They have a specific shape related to function.
• A specified reaction is triggered when a substrate with a matching shape attaches at the active site.
• The process of breaking molecules down are sped up by enzymes.
(Wolfe, 2000)
• Examples of enzymes from fructose metabolism: Aldolase B & Fructokinase
(Hudon-Miller, Enzymes, 2012)
HEREDITARY FRUCTOSE
INTOLERANCE
• Fructose metabolism starts with fructokinase breaking it down to produce fructose-1-phosphate (F-1-P). F-1-P is also a signal sender to glucokinase (the enzyme used to break down glucose) if blood sugar is high. F-1-P is broken down by the enzyme Aldolase B to make DHAP + glyceraldehyde. These products are used in glycolysis to produce ATP or in gluconeogenesis.
• Aldolase B being unable to take the substrate F-1-P and turn it into DHAP + glyceraldehyde leads to Hereditary
Fructose Intolerance (HFI).
• Fructose will still be phosphorylated by fructokinase resulting in F-1-P. Because the Aldolase B is deficient and not doing it’s job, the F-1-P builds up. This build up leads to F-1-P to keep sending signals for glucokinase to come back out of the nucleus into the cytoplasm to keep breaking down glucose. This leads to a cycle and a decrease in glucose being able to released back into the system. Eventually, you become hypoglycemic. The symptoms include: shaking, irritability, & nausea.
• Another complication is with free phosphate pools in the cell decreasing. Frucktokinase will still be functioning and producing F-1-P. The phosphate is stuck and this continues. The free phosphates in the cell are necessary in the electron transport chain (ETC) to change ADP to ATP. Slow ATP production leads to liver cells being low on energy and liver failure.
• Downstream effects of Aldolase B deficiency can be responsible for HFI by: inhibition of glucose production and reducing the generation of ATP in the ETC.
(Sanders, 2013)
LOCK AND KEY MECHANISM
OF ENZYME ACTIVITY
ACTIVATION OF ENERGY
ENZYMES EFFECTS
(Activation, n.d.)
ALDOLASE B
• The first step in fructose metabolism is where the enzyme fructokinase into Fructose1-phosphate (F1P) .
• The second step in the fructose metabolism pathway is where Aldolase B is important. In this step, the fructose-1-phosphate (F1P) is broken down by the
Aldolase B. This results in two molecules: glyceraldehyde and dihydroxyacetone phosphate. • Products of this reaction (DAP) participate in the pathway of glucose metabolism.
(Carbohydrate, n.d.)
CORI CYCLE
• Intense muscular activity is when the Cori Cycle will begin. Exercise is an example of this.
• Lactic acid will be created by glycogen in the muscles being broken down.
• Lactic acid will be converted to glucose in the liver.
• Glucose will then be transferred to the muscles to be used for energy.
• Once the muscular activity has ceased, the muscles can store glucose.
• The Cori Cycle is temporary. This cycle shifts metabolic activity from the muscles to the liver.
• More ATP would be used rather than created if the Cori Cycle took place in a single cell.
(Muscular, n.d.)
CITRIC ACID CYCLE
respiration:
(Hudon-Miller, Citric, 2013)
HYPOTHETICAL DEFECT
• A defect in the Citric Acid Cycle makes the cycle unable to be completed and produce side products needed for the electron transport chain.
• Citrate synthase is an enzyme in the Citric Acid Cycle. It participates in the reaction of making Citrate.
• Citrate is used to make more CoA. CoA is needed to make new Acetyl CoA to keep the cycle going.
• A defect in citrate synthase would cause the cycle to never get passed this step, therefore preventing NAD+,GDP, and FAD+ from becoming NADH,H+,
GTP, and FADH2. If the Electron Transport Chain cannot get access to these, then ATP cannot be made.
(Hudon-Miller, Citric, 2012)
