enzyme

• enzyme - most effective catalyst known
• human has 1000s enzymes
• most enzymes are glubular protein
• enzymes are affected by the alteration of

  • pH
  • temperature
  • protein denaturants
• enzymes that are now known are made of RNA
• two structures of enzyme

  1. simple - protein only (aa chain)
  2. conjugated - nonprotein added to protein
• under conjugated enzyme are

  • apoenzyme - protein part
  • cofactor - nonprotein part
  • holoenzym - biochemically active (apoenzyme + cofactor)
• cofactor provide additional chemically reactive functional group
• categories of cofactor:

  1. simple metal ion - supplied through dietary mineral intake
  2. small organic molecule - "coenzyme", serves as cofactor
• conenzyme are formed in human body using building blocks (B vitamin)
• permanenty bond cofactor - coenzyme FAD (riboflavin)
• temporary bond cofactor - coenzyme NAD+ (niacin)
• nomenclature of enzyme

  • suffix -ase, identifies as enzyme (enzyme designation)
  • suffix -in, found in first enzymes studied (digestive enzyme)
  • type of reaction - prefix
  • substrate - addition to type of reaction
• six major classes of enzyme

  1. oxidoreductases - oxidation reduction
  2. transferases - transfer of function groups
  3. hydrolase - hydrolisis
  4. lysases - addition or removal of group ; to form double bond
  5. isomerase - rearrangement ng atom
  6. ligases - bond formation, ATP
• subtype of transferase

  1. transaminases - amino group
  2. kinases - phosphate group
• enzyme active site - small part of the structure that is involved in catalysis
• enzyme active site is a 3D formed by groups from different parts of protein chain (by folding and bending)
• enzyme active site is the crevicelike location
• enzyme subtrate complex is an intermediate reaction species that forms when substrate binds with the active site
• two models for substrate binding

  1. lock and key model - enzyme is fixed, only substrate that has a specific shape can bind (simpliest)
  2. induced fit model - enzymes shape allows small changes
• enzyme specificity:

  • absolute specificity - one reaction only ; most restrictive
  • sterepchemical specificity - particular stereoisomer
  • group specificity - same functional group
  • linkage specificity - particular type of bond ; most general
• temperature

  • higher temp = higher rate
  • optimal temp reached = enzyme activity decreases
• pH

  • drastic change = denaturation
  • optical activity pH range: 7 to 7.5
• substrate concentration

  • constant concentration = higher activity

  substrate saturation

  • reaches maximum = active sites are full

  turnover number

  • number of substrate molecule converted to product per second
• enzyme concentration

  • constant concentration = high enzyme activity = high enzyme concentration
• enzyme inhibition slows down or stops normal catalytic function by binding into the enzyme

  • competetive - competes with substrate for the active site
  • noncompetetive - cause change in structure and prevents enzyme activity ; binds to enzyme at a location other than active site
  • irreversable inhibition - inactivates (permanent) enzymes by forming a strong covalent bond with the active site
• regulation of enzyme activity

  • allosteric device
  • feedback control
  • proreolytic enzyme and zymogen
  • covalent modification of enzyme
• allosteric enzme

  • responsible for regulating cellular process
  • have quarernary structure - two or more protein chain
  • have two binding site - for substrate and regulator ; different from each other (location and shape)
  • binding molecule at regulatory site causes changes in 3d structure of enzyme
  • substance the bind at regulatory site : regulators
• feedback control - process of activation/inhibation wherein the first reaction is controlled by a product of the reaction sequence
• covalent modification of enzyme

  • 3rd mechanism
  • enzyme activity is altered by covalently modifying structure of enzyme through attachment/removal of chemical group from particular amino acid
• proteolytic enzymes and zygomens

  • 2nd mechanism
  • production of enzyme in an inactive form (zygomen, proenzyme) ; turned on at the appropriate time and place
  • proteolytic enzyme: inactive form to active form if needed ; breaks peptide bond