dr. JANGKI HASHUMALDEPARTEMENT OF BIOCHEMISTRYFACULTY OF MEDICINEHASANUDDIN UNIVERSITY

DEFINISINOMENKLATUR DAN KLASIFIKASIINTERAKSI ENZIM-SUBSTRATKOFAKTOR DAN KOENZIMPENGARUH pH DAN SUHUCONTOH ENZIM SPESIFIK

DEFINISIEnzim adalah biokatalisatorBiological sistem hidupSubstansi yang meningkatkan kecepatan reaksi kimia tanpa mengubah hasil

BiokatalisatorProtein dengan molekul besarPermit reactions to go at conditions that the body can tolerateCan process millions of molecules every secondAre very specific react with one or only a few types of molecules (substrate)Substrate is a substance that is acted on by an enzyme

NOMENCLATURE AND CLASSIFICATIONEnzyme nomenclature is based on :What it reacts withHow it reactsAdd ase endingExamples :Lactase : enzyme that reacts with lactosePyruvate decarboxylase : removes carboxyl from pyruvate

Enzyme usually written in trivial name but every enzyme has an official name from International Union of Biochemistry (Enzyme Nomenclature 1992)Based on the official nomenclature system, each enzyme has a full name and an enzyme commission number (E.C) derived in the position in the classification schemeExample :Hexokinase has the full name ATP: D-hexose 6-phosphotransferase and the classification number E.C 2.7.1.1

Classification of enzymesBased on type of reaction, enzymes have been classified to six major classes as follows :Oxidoreductases : catalyze oxidation-reduction reactionsTransferases : catalyze transfer of functional groups fron one molecule to anotherHydrolases : catalyze hydrolytic cleavage

Lyases : catalyze removal of a group from or addition of a group to a double bond, or other cleavages involving electron rearrangmentIsomerases : catalyzed intramoleculer rearrangementLigases : catalyzed reactions in which two molecules are joinedIsozim : enzim yg mempunyai fungsi katalitik yg sama tetapi strukturnya berbeda.

ENZYME-SUBSTRATE INTERACTION

UNCATALYZED REACTION

EN GE SUBSTRATE RG PRODUCTY

VELOCITY

Effect of enzyme on activation energy :All reaction must get over the activation energy hurdle

CATALYZED REACTION

ENER SubstrateGY Product

VELOCITY

Enzyme change how a reaction will proceedEnzyme menurunkan energi aktivasiAnd it makes the reaction faster

Effect of substrate concentration:For non-catalyzed reaction:Reaction rate increase with concentrationFor enzyme catalyzed reaction :Also increase, but only to a certain point Vmax- maximum velocityAt Vmax, the enzyme is working as fast as possible

Karakteristik dari sisi aktif enzim :Sisi katalitikTempat reaksi katalitis terjadi Sisi ikatanArea pengikatan substratEnzim bekerja lemah, non-kovalen, interaksi berikatan dgn substrat pada tempat tertentu dari rantai R dari asam aminoSisi adalah kantong or cleft pada permukaan enzim.

Langkah2 reaksi melibatkan enzim :Enzim dan substrat berkombinasi pada sebuah kompleksKompleks bergerak pada transition state A complex of the enzyme and the product is producedEnzimdan produkterpisah

Karakter sisi aktif enzim :Lock and key modelDikemukakan oleh Emil Fisher (1890)Model ini mengasumsikan bahwa hanya a substrat yang memiliki struktur atau bentuk yang sesuai, yang bisa berikatan dgn enzim.

Induced-fit modelDikemukakan oleh Daniel Koshland (1958)Model ini mengasumsikan adanya perubahan dari sisi aktif enzim untuk berikatan dengan substrat.Model ini menggambarkan adanya fleksibilitas dari struktur enzim.Berdasarkan model ini, enzimmampu menyesuaikan diri dengan model substrat.

Kofaktor dan Koenzim

Komponen bukan protein disebut kofaktor. Kofaktors dapat terdiri organik atau inorganic compounds. Jika kofaktornya organik, disebut koenzim. Koenzim adalah molekul kecil dibandingkan dengan bagian protein dari enzim. Banyak koenzim yang diturunkan dari vitamin. Sedangkan jika anorganik merupakan metal ions. (e.g. Ca, Cu, Co, Fe)

Enzim yang butuh a kofaktor, tapi tidak memiliki ikatan yang disebut apoenzim. Sebuah apoenzim yang berikatan dgn kofaktornya disebut holoenzyme (i.e., the active form)

COENZYME + SUBSTRATE NO PRODUCT

APOENZYME + SUBSTRATE NO PRODUCT

APOENZYME + COENZYME + SUBSTRATE PRODUCT

HOLOENZYME

Some vitamins that are often converted to coenzymes :

VitaminCoenzymeFunctionB1 (Thiamine)Thiamine pyrophosphate DecarboxylationB2 (Riboflavin)Flavin adenine dinucleotide (FAD)Carries hydrogenB3 (Niacin)Nicotinamide adenine dinucleotide (NAD) Oxidation or hydrogen transfer Folic acidTetrahydrofolic acidAmino acid metabolismPantothenic acidCoenzyme AAcyl group carrier

EFFECT OF pH & TEMPERATURE ON ENZYMATIC REACTIONSExceeding normal pH and normal temperature ranges always reduces enzyme reactions ratesTemperatur optimumnya umumnya 25-40CEnzim bekerja pada pH 7

Temperature

pH

SPECIFIC ENZYME EXAMPLECHYMOTRYPSINA proteolytic enzyme Digestion of dietary protein in small intestineInitially produced in an active form (zymogen) : chymotrypsinogen; and actived by tripsinChymotripsin only works on amino acids containing an aromatic ring (phenylalanin, tyrosine, tryptophan)

CONCLUSION ENZYME DEFENITION ENZYME NOMENCLATURE AND CLASSIFICATIONENZYME-SUBSTRATE INTERACTIONCOFACTOR AND COENZYMEEFFECT OF pH TEMPERATURE

REFERENCESBrownie AC, Kernohan JC. Biochemistry. A core text with self-assesment. Churchill Livingstone, 1999.Campbell PN, Smith AD. Biochemistry Illustrated 4th ed. Churchill Livingstone, 2000.Mathews CK, van Holde KE, Ahren KG. Biochemistry 3th ed, Addison-Wesley Publishing Company, 2000.Swaminathan R. Handbook of Clinical Biochemistry. New Delhi. Oxford University Press, 2004.

Kegunaan :Menentukan prognosis Menentukan diagnosa penyakit herediterDipakai untuk terapi