CHAPTER - 5 | Enzymes
transfer of one carbon units between substrates. Formimino group of formiminoglutamate is transferred to FH4as shown below. Formiminoglutamate+FH4
Glutamate + Formimino FH4.
Formimino group of formiminoFH4 is later transfered to other substrates. d. Coenzymes involved in transfer of groups: Methyl cobamide coenzyme of vit. B12 is involved in methyl group transfer. CoenzymeA coenzyme of pantothenic acid is involved in CoA transfer reactions. Methionine synthase transfers methyl group of methyl cobamide as shown below. Homocysteine +methylcobamide
Methionine + cobamide
Acyl-CoA synthatase catalyzes transfer of CoA to fatty acid as shown below. Fatty acid +CoA+ATP
Acyl-CoA+AMP+PPi
e. Nucleotide coenzymes : Many nucleotides function as coenzymes. They are ATP, GTP, CTP, ADP, GDP, CDP, PAPS and SAM. Metals Enzymes in which metal is part of enzyme molecule are known as metalloenzymes and metal is attached through coordinate bond. More over metal takes part in catalysis. Removal of metal leads to loss of catalytic activity of enzymes. Cytochrome oxidase, catalase, succinate dehydrogenase are examples for iron metallo enzymes. Metal dependent enzymes Are those enzymes in which metal is not part of enzyme molecule but it is required for catalysis. It act as bridge between enzyme and substrate. In the absence of metal enzyme is unable to form enzyme substrate complex. Hexokinase, galactokinase and pyruvate kinase are dependent on magnesium for activity. Metal activated enzymes In presence of metals activity of these enzymes is increased to many folds. In the absence of metal they catalyze reaction but at low rate. Chloride is an activator of amylase and angiotensin converting enzyme. Calcium is an activator of trypsin.
8. Define isoenzymes. Give examples. How they are separated? A. Isoenzymes are multiple forms of an enzyme. They catalyze same reaction but differ in physicochemical properties. They may occur among organs, species. They are present in blood and other fluids. Isoenzymes of several dehydrogenases, transaminases and phosphatase are identified. Lactate dehydrogenase Isoenzymes Lactate dehydrogenase is a oligomeric enzyme. It is a tetramer. Made up of two types of sub
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