2. Enzyme Inhibitors
• A variety of chemicals can act as enzyme inhibitors, inactivate enzyme
transiently or permanently
• Competitive inhibitor
• Chemical directly competes with the substrate for catalytic site and prevents
the enzyme from forming products
• Such molecules resemble normal substrates
• Bacterial growth is inhibited by sulfa drugs which are similar to p-
aminobenzoate, drug compete with p-aminobenzoate for catalytic site in folic
acid synthesis. This blocks the production of folic acid and no nucleic acid
formation
• Noncompetitive inhibitors
3. Enzyme Inhibitors
• Noncompetitive inhibitors
• Such chemicals bind to the enzyme not on catalytic site but some location
which changes enzyme’s shape(forms covalent bonds in a.a) making it inactive
or less active
• Do not directly compete with the substrate, e.g. Pencillin bind to
transpeptidase in bacteria to inhibit cell wall synthesis.
• Other inhibitors are metals:
4. Regulation of Metabolic pathways
Three major approaches
• Metabolic channeling- pathway activity is regulated by localizing
metabolites and enzymes into different parts of cell
• Regulation of the concentration of enzyme by its synthesis-slow
• Direct stimulation or inhibition of the activity of critical enzyme-
rapidly alters pathway
5. Two general approaches to control enzymatic
activity.
Amount or availability of the enzyme or regulate the catalytic activity
• Enzyme’s concentration in a cell depend upon the rate in which it is
synthesized and the rate it is degraded.
• Synthesis rates can be transcriptionally or translationally controlled.
• Degradation rates of proteins are also controlled.
6. Metabolic reactions are controlled by the presence
or absence of particular enzymes in pathways
• If appropriate enzyme is present then reaction continues or if the
appropriate enzyme is absent then pathway stops
• Some Enzymes are constitutive or inducible
• Only required at certain times to prevent resources being wasted, genes can be
switched on and off.
• Enzyme rate regulated at the genomic level
• level of gene expression (control of the number of enzyme molecules)at a level
of enzyme action (change of enzyme shape)
7. Metabolic channeling
• Most common is compartmentation for differential distribution of
enzymes and metabolites
• Enzymes and substrate can move
• Unicellular bacteria and archaea different areas of cytoplasm even in:
• Periplasm and mesosomes
• Eukaryotes(fungi, algae and protozoa)-organelles
• Fatty acid catabolism is located within the mitochondrion and fatty acid
synthesis in the cytoplasmic matrix.
8. Regulation of pathways by Metabolic
channeling
• Concentration of enzyme and substrate affect enzyme activity.
• Substrate concentration 10-3 to 10-6 moles/liter or lower
• Under these conditions the concentration of an enzyme’s substrate
control its activity , more substrate more product form rapidly
• If more than two enzymes in different pathways use the same
metabolite then enzymes compete for substrate, enzyme with lowest
Km value for the substrate will be use it
9. Regulation of pathways by controlling
enzyme activity
• Post translational control of enzymes which can be irreversible and
reversible types
• Irreversible by degradation of enzymes to activate or inhibit activity
• Reversible by allosteric regulation and covalent modification.
• Allosteric enzyme’s activity is altered by effector or modulator
• Effector binds reversibly by noncovalent forces to a regulatory site separate from the
catalytic site and result in conformational changes in enzyme and catalytic site
• Negative are positive effector to suppress or enhance enzyme’s activity
• Enzymes can be switched on and off by reversible modification when
functional group is added or removed like phosphate, methyl, uridine,
adenine and adenosine diphosphate ribosyl etc
10. Pathways control by feedback inhibition
• Most metabolic pathways’ rate is control by regulatory enzyme’s activity
• Every pathway has at least one pacemaker enzyme that catalyzes the
slowest or rate-limiting reaction in the pathway
• Other reactions proceed more rapidly compare to pacemaker reaction but
pace maker enzyme activity directly alter pathway’s speed
• Pacemaker enzymes’ reaction is mostly first step in a pathway
• The end product of the pathway often inhibits this enzyme-feedback
inhibition or end product inhibition
• Feedback inhibition ensures balanced end product formation.
• If end product concentration decreases, it is activity is again initiated
• This inhibition automatically regulate end product supply with the demand
11.
12.
13. Do enzymes regulate metabolism only
no
Enzymes also regulate various functions
like transport, movement, replication,
cell division, reproduction etc.
14. Enzymes in other functions like chemotaxis
• All prokaryotic or eukaryotic microorganisms detect nutrients, toxins or
other chemicals in their environment
• Depending upon chemical if required or harmful, microbes either move
toward them or away from it (attractant or a repellant)
• For example, both glucose and glycerol are metabolized but
only glucose is an attractant
Structural recognition of attractant by receptors
16. Bacterial cells adapt to changing environmental
conditions to ensure survival including chemotaxis
• A number of receptors are involved in it
• Receptors sense and using signal transduction pathways to react
• Most common pathways are one-component systems then two-component
systems
• Also chemoreceptor-based signaling cascades(referred chemotaxis or
chemosensory systems)
• Chemosensory pathways not only mediate chemotaxis but also type IV
pilus-based motility and regulate many cellular processes
• Methyl-accepting chemotaxis proteins (MCPs)perform with other protein
like transducer-like proteins or Tlps, CheA histidine kinase and the CheW as
coupling protein
• Chemoreceptors recognize chemical, this information is transmitted
19. Enzymes and Proteins in chemotaxis
• Best researched such system is chemotactic system in E.coli
• E. coli move forward in swimming motion called a run and tumbling
motion
• Run occurs when the flagella rotates in a counterclockwise direction
(CCW) and a tumbles when flagellum rotates clockwise(CW)
• Tumbling movement set direction for run
3D Random Walk
EM
