FBICH 410 1st Edition Lecture 23Outline of Last Lecture - Enzymes ChemistryOutline of Current Lecture - Proteolytic enzymes- hydrolytic enzymeso 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 protono 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 proteaseo 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 Regulationo Regulated by: availability of S and P, rate of synthesis and degradation, allosteric rxn, covalent modification, zymogens, isozymeso Zymogen- precursor of enzymes- proteolytic cleavage converts zymogen to active form Process is irreversible- once activated always activatedo 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 subunitso 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 enzymesThese 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 rxno 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- Membraneso Help accumulate nutrients, carry out transduction, facilitate cell motion, assist in reproduction, modulate signal transduction, mediate cell cell interactions, barriero 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 transverseo 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 proteino 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 proteinso 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)