F BICH 410 1st Edition Lecture 23 Outline of Last Lecture Enzymes Chemistry Outline of Current Lecture Proteolytic enzymes hydrolytic enzymes o Aspartic proteases 2 active sites for Asp Kinetic mechanism ping pong Initial velocity plot has parallel lines Chemical mechanism Acid Base catalysis General acid proton donor General base abstracts proton o Initial velocity plot intersecting o HIV Proteases cell translate HIV mrna protein then must be broken down in order for viral growth and cellular infections Drug for AIDS inhibitors of HIV protease o Carboxyl peptidase cleaves of AA residue on C term Arg there to stabilize COO with ionic interactions Zn present indicating metal ionic catalysis Glu is a weak nucleophile therefore C has to be a strong electrophile which is why Zn is used Sequential rxns have all substrates bound and then releases all products Enzyme Regulation o Regulated by availability of S and P rate of synthesis and degradation allosteric rxn covalent modification zymogens isozymes o Zymogen precursor of enzymes proteolytic cleavage converts zymogen to active form Process is irreversible once activated always activated o Isozymes similar but not the same AA seq Each catalyzes same bich rxn but differ in kinetics Different kM and Vmax Ex hexokinase heart and glucokinase liver can have 4 liver subunits or a mix or 4 heart subunits o Allosteric regulation must have multi subunits ie hemoglobin Enzymes that have allosteric regulation sigmoidal Michaelis menton enzymes hyperbolic Allosteric don t obey michaelis menton plot Simplest model T inactive and R active Act as regulatory enzymes in pathways Feedback inhibition product inhibits initial enzymes These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Feedforward inhibition product actives enzymes in forward rxn o Covalent modifications reversible covalent changes to specific AA side chains Enzymes are used to convert regulatory enzymes to either active form of inactive form through covalent modifications Often times caused by hormonal regulation Ie phosphorylation Membranes o Help accumulate nutrients carry out transduction facilitate cell motion assist in reproduction modulate signal transduction mediate cell cell interactions barrier o Composition bio membranes contain protein and lipids Proteins catalyze rxn mediate flux of nutrient and waste and participate in relaying external info to cell Protein to lipid ratios vary with membrane function Membrane structure and assembly phospholipid bilayer is fluid matrix Lipid and proteins can move via rotation and lateral movements but not transverse o Peripheral membrane proteins globular and easily dissociated loosely associated Amphipathic alpha helix polar and nonpolar face H bonded and ionic interacting proteins Hydrophobic loop Association with integral protein o Integral proteins tightly associated req detergents or chaotrophic agents separate from membrane Tightly associated and water insoluble Transmembrane helical protein go all the way through membrane Typically C term inside and N term outside Carbohydrates attached to outside All residues within alpha helix hydrophobic Most transmembrane proteins are multi spanning with 2 12 segments AA locations hydropathy scale plot P in helix induces kinks causing weak pt which might facilitate movement req for TM transport channels Beta sheet TM proteins from barrels Novel helical barrels All integral proteins are not transmembrane proteins o Lipid linked proteins proteins can associate with membranes through covalent attachment to lipids that anchor the protein Some behave as soluble proteins Others remain with membrane association even if anchor is removed Linkage can be reversible thus acting as a switch device Four types which are always on cytoplasmic side Thioester linked fatty acyl anchor generally palmitate and reversible Amide linked myristoyl anchor used for HIV drugs Thioester linked prenyl anchor built on isoprene unit Glycosyl phosphatidylinositol GPI anchors