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Chapter-03 Enzymology

BOOK TITLE: Textbook of Biochemistry for Dental Students

Author
1. Vasudevan DM
2. S Sreekumari
3. Vaidyanathan Kannan
ISBN
9789350254882
DOI
10.5005/jp/books/11333_3
Edition
2/e
Publishing Year
2011
Pages
12
Author Affiliations
1. Faculty of Medicine, Amrita Vishwa Vidyapeetham, (Amrita University), Kochi, Kerala, Formerly Principal, College of Medicine, Amrita, Kerala; Formerly, Dean, Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim, Amrita Vishwa Vidyapeetham (Deemed University), Cochin, Kerala, E-mail: dmvasudevan@aims.amrita.edu, PG Programs and Research College of Medicine, Amrita Institute of Medical Sciences, Kochi, Kerala, India, College of Medicine, Amrita Institute of Medical Sciences, Kochi, Kerala, India; Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim, India
2. Jubilee Mission Medical College, Trissur, Kerala, Sree Gokulam Medical College and Research Foundation, Thiruvananthapuram, Kerala, India, Jubilee Mission Medical College and Research Institute, Thrissur, Kerala, India, Government Medical College, Thrissur and Thiruvananthapuram, Kerala, India; Sree Gokulam Medical College and Research Foundation, Thiruvananthapuram, Kerala, India; Jubilee Mission Medical College and Research Institute, Thrissur, Kerala, India
3. Amrita Institute of Medical Sciences, Kochi, Kerala, India, Pushpagiri Institute of Medical Sciences and Research Centre, Thiruvalla, Kerala, India, Believers Church Medical College and Hospital, Thiruvalla, Kerala, India
Chapter keywords

Abstract

Almost all known enzymes are proteins. According to IUBMB, enzymes can be classified into (i) Oxidoreductases (e.g. Alcohol dehydrogenase), (ii) Transferases (e.g. Hexokinase), (iii) Hydrolases (e.g. Acetyl Cholinesterase), (iv) Lyases (e.g. Aldolase), (v) Isomerases (e.g. Triose Phosphate isomerase), and (vi) Ligases (e.g. Acetyl-CoA carboxylase). Enzymes may be simple or compound proteins. In case of compound proteins, the protein component is termed ‘apoenzyme’ and the prosthetic group is termed ‘coenzyme’. The combination produces a functional ‘holoenzyme’. Coenzymes are mainly constituted by the B complex group of vitamins. Coenzymes may be involved in the transfer of hydrogen (e.g. NAD, FAD, FMN) or groups other than hydrogen (e.g. amino group by PLP, hydroxyethyl group by TPP). Enzymes requiring the presence of a certain metal ion for their activity are called metalloenzymes. Examples are zinc in carbonic anhydrase, iron in catalase and peroxidase, calcium in lipase etc. Michaelis-Menten theory states that an enzyme (E) combines with a substrate (S) to form an enzyme-substrate (E-S) complex, which breaks down to give product (P). Theories proposed to explain the mechanism of enzyme action are Fischer’s Template (lock and key) theory and Koshland’s induced fit theory. Area of an enzyme where the catalysis occurs is called the ‘active site’. Enzyme activity is influenced by enzyme concentration, substrate concentration, pH, temperature and presence of inhibitors. Iso-enzymes are physically distinct forms of the same enzyme activity. Clinically useful enzymes in diagnosis and prognosis of myocardial infarction are CK-MB. ALT and ALP are clinically useful markers in hepatic diseases. ALP is also a useful marker in bone diseases. ACP and PSA are used in the diagnosis of prostate cancer.

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