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| G = G(prime)' + R T ln(Products/reactants) |
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catalyze oxidations and reduction reactions such as the conversion of succinate to fumarate (succinate dehydrogenase). An example is the oxidation of lactate to pyruvate catalyzed by lactate dehydrogenase.
ex. Lactate dehydrogenase |
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Definition
catalyze transfer of groups such as methyl or glycosyl groups from a donor molecule to an acceptor molecule. An example is the conversion of serine to glycine catalyzed by serine hydroxymethyl transferase.
ex. Serine hydroxymethyl transferase |
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Definition
catalyze the hydrolytic cleavage of C-C, C-O, C-N, P-O, and certain other bonds, including acid anhydride bonds. An example is the hydrolysis of urea to CO2 and NH3 catalyzed by urease.
ex. Urease |
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Definition
catalyze cleavage of C-C, C-S, C-O, C-N, and other bonds by elimination, leaving double bonds, and also add groups to double bonds. An example is the decarboxylation of pyruvate to acetaldehyde catalyzed by pyruvate decarboxylase
ex. Pyruvate decarboxylase |
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Definition
catalyze geometric or structural changes within a single molecule, such as the conversion of citrate to isocitrate by aconitase. An example is the isomerization of methylamlonyl CoA to Succinyl CoA catalyzed by methylmalonyl CoA mutase.
ex. Methylmaloney-CoA mutase |
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Definition
catalyze the joining together of two molecules, coupled to the hydrolysis of a pyrophosphoryl group in ATP or a similar nucleoside triphosphate. An example is the carboxylation of pyruvate to form oxaloacetate catalyzed by pyruvate carboxylase.
ex. pyruvate carboxylase |
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Term
| Some examples of prosthetic groups |
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Definition
| Some examples of prosthetic groups are shown in the diagram. Flavin mononucleotide (FMN) is a prosthetic group found in many flavoproteins, such as cytochrome P450 reductase. Pyridoxal phosphate is found in enzymes that catalyze transamination reactions and NAD+ functions as a coenzyme in many oxidation-reuction or redox reactions, such as those in the TCA cycle. |
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| Lineweaver-Burk intercepts |
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Definition
x-intercept: -1/Km
y-intercept: 1/Vmax
y axis = 1/Vo
x axis = 1/[S] |
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Definition
| 1/v = Km/Vmax [S] + 1/Vmax |
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| Enzyme Inhibition-Competitive (Km and Vmax) |
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Definition
Vmax is the same
Km is increased |
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| Enzyme Inhibition-Noncompetitive (Km Vmax) |
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Definition
Vmax is decreased
Km is the same |
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Definition
| Sigmoid substrate vs. velocity plot. Effectors can move the plot left (rate increase) or right (rate decrease) by shifting the Km for substrate. |
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Term
Regulatory event
Substrate availability |
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Definition
Effector Results Time
Substrate
Change in velocity
Immediate |
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Term
Regulatory event
Product inhibition |
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Definition
Effector Results Time
Product
Change in Vmax and/or Km
Immediate |
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Term
Regulatory event
Allosteric control |
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Definition
Effector Results Time
End product
Change in Vmax and/or Km
Immediate |
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Term
Regulatory event
Covalent modification |
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Definition
Effector Results Time
Another enzyme
Change in Vmax and/or Km
Immediate to minutes |
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Term
Regulatory event
Synthesis or degradation of enzyme |
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Definition
Effector Results Time
Hormone or metabolite
Change in [enzyme]
Hours to days |
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Definition
| 1. Compartmentation of enzymes within specific organelles is an example of permanent regulation achieved through physical separation of competing metabolic pathways within subcellular compartments. It provides controlled access of substrates to their enzymes. For example, enzymes that synthesize fatty acids are located in the cytosol, whereas those that oxidize fatty acids are located in the mitochondrial matrix. Other examples include the location of alkaline phosphatase (cell membranes), aspartate aminotransferase in mitochondria, γ-glutamyl transferase in the smooth endoplasmic reticulum and myeloperoxidase location in lysosomes. |
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Definition
This is long-term regulation of metabolism; changes in gene expression leading to increased or decreased enzyme synthesis (i.e., induction or repression) can provide long-term regulation but has relatively slow response time varying from hours to days. The genes for multiple enzymes in a metabolic pathway are often regulated together.
Examples include the synthesis of fat-metabolizing enzymes in skeletal muscle is induced in response to aerobic exercise conditioning. |
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Definition
This is rapid regulation, taking only seconds to minutes. Enzymes in opposing pathways are reciprocally regulated to prevent futile cycles. Reversible phosphorylation and dephosphorylation is a common mechanism by which hormones regulate enzyme activity. Kinases phosphorylate serine, threonine, or tyrosine residues in regulated enzymes; phosphatases remove the phosphate groups (dephosphorylation). Reversible phosphorylation and dephosphorylation, often under hormonal control (e.g., glucagon), increases or decreases the activity of key enzymes.
Examples include glycogen phosphorylase which is activated by phosphorylation (protein kinase A), whereas glycogen synthase is inhibited. |
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Definition
| This is instantaneous regulation. Allosteric regulation can rapidly (seconds to minutes) increase or decrease operation of a metabolic pathway. Allosteric effectors are usually end-products of the regulated pathway and, therefore, do not resemble the substrate for the enzyme. The regulated enzymes catalyze rate-limiting, often irreversible, steps at the beginning of metabolic pathways. Examples include cytidine triphosphate, the end-product of the pyrimidine biosynthetic pathway, inhibits aspartate transcarbamoylase, the first enzyme in this pathway (feedback inhibition). |
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Definition
| in which a series of enzymes sequentially activate each other, can amplify a small initial signal, leading to a large response. Examples include the binding of glucagon to its cell surface receptor on liver cells triggers a cascade that ultimately activates many glycogen phosphorylase molecules, which each catalyze production of numerous glucose molecules. This leads to a rapid increase in blood glucose. |
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Definition
| Proenzymes or zymogens, are inactive storage forms that are activated as needed by proteolytic removal of an inhibitory fragment. Digestive proteases, such as pepsin and trypsin, are initially synthesized as proenzymes (e.g., pepsinogen and chymotrypsinogen) that are activated after their release into the stomach or small intestine. In acute pancreatitis, activation of zymogens (e.g., alcohol, hypercalcemia) leads to autodigestion of the pancreas. |
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Definition
| o Ethanol is the alcohol least toxic to humans. Ingestion of methanol can lead to blindness and acidosis. Propanol and higher alcohols are more toxic than ethanol but are rarely abused. Ethylene glycol, a common ingredient in antifreeze, is also toxic. Ethanol is metabolized to acetaldehyde in the liver by the enzyme alcohol dehydrogenase. Acetaldehyde is quite toxic and is rapidly metabolized to acetic acid by another enzyme (acetaldehyde dehydrogenase). |
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Definition
| o HIV protease illustrates catalysis by an enzyme that lowers the activation barrier by stabilizing a transition state intermediate. |
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