METABOLISM, ENZYMES AND KINETICS

rvsd 10/12/92, \10/6/93, 7/15&18/94, 7/17/98 2 June 99, 18 July 01, 17 Jan 02, 12 July 02, 16July04, 15July05

B&D P. 132-, tfc: 101-, Alcamo p 121-126, 697, TFC 7^th: 113-133, 8^th: 111-148, Black 6^th: 113-125, Bauman, 123-138

METABOLISM: (p 124) Sum of catabolism (degradative) and anabolism (biosynthetic)

Products contain less energy than reactants, (ΔG = negative), why doesn't rxn go? Need activation energy.

Illustrate reaction profile: (p 129) energy content curve vs time for chem reaction with and without catalyst.

Reaction energy versus activation energy: metastable state: lack of stable intermediates

catalysts stabilize intermediates, reduce activation energy, therefore speed up reactions

Pasteur found that yeast were necessary for grape juice to be fermented.

Buchner brothers (1897) preparing yeast extract for nutritional supplement. Used sugar as preservative. Noted alcoholic aroma and taste days later. Demonstrated it was in vitro fermentation, found agents inside yeast performed chemical changes: called en-zymes (inside yeast)

In biological systems, catalysis is performed by protein catalysts = enzymes

Enzyme:           apoenzyme       [detach] =                       protein component of enzyme

(p. 128)             prosthetic         [onto, place] group =     cofactor (inorganic) or coenzyme (organic)

                          holoenzyme      [entire] =                        entire functional enzyme

Active site binds substrate. (P. 130) Substrate specificity high in biological systems

Induced fit, lock and key for substrate: enzyme grasps substrate, substrate causes conformation change

prosthetic groups:   organic:        coenzymes:      NAD, FAD, Coenzyme A, FMN (many vitamins)

                                  inorganic:     cofactors:         metal ions: Fe, Mg, Ca, Mn, Zn,, most trace elements required by organisms used for this purpose

Four levels of protein structure lead to precise folding. (Review p 48)

Proper folding critical for activity: (p 131) temp, pH, heavy metals alter configuration (note optima)

KINETICS: GRAPH: Vmax, substrate saturation (Lucille Ball, candy factory)

Competitive (p 132) versus Allosteric (p 133) inhibitors:

             binding and effects analogs of substrate compete for active site

velocity (rate of reaction) vs [S] shows saturation. Show normal, competitive & non competitive inhibitors:

             competitive: sulfanilamide drugs inhibit binding of pABA in folate synthesis.(p 132)

             allosteric (end-product inhibition, p 134): metabolic pathways regulate commitment of resources.

Note: High [S] overcomes competitive inhibition, but not allosteric inhibition

Irreversible inhibition             1) heavy metals bind to -SH groups often at active sites

                                                  2) halogens add at tyrosine side chains,

                                                  3) alkylating agents, bind covalently to enzyme, destroy catalytic activity.

Required for enzyme activity:

                                                  conditions for enzyme inhibition (antibacterial, preservation from spoilage)

             enzyme & substrate

             water                            dehydration, hyperosmotic conditions

             cofactors                       EDTA removes divalent cation metals,

             coenzymes                   sulfanilamide drugs inhibit binding of pABA in folate synthesis.(p 118)

             proper temp                  refrigeration, pasteurization

             proper pH                     pickling

             proper S-S bonds          heavy metals bind to sulfhydryls

             proper -OH bonds        iodine and other halogens

Illustrate pH optimum curves for pepsin, sucrase, alkaline phosphatase

Remind that optimum temperatures for psychrophile, mesophile, thermophile reflect those needed for enz.