Introduction to Biotransformation (Metabolism) - Pesticide Biotransformation and Disposition - page 52

4

CHAPTER

Introduction to Biotransformation
(Metabolism)

Ernest Hodgson
North Carolina State University, Raleigh, NC, USA

Outline
Introduction

53

Reactions Catalyzed in Xenobiotic Metabolism 54

Xenobiotic-Metabolizing Enzymes 54

Phase I Xenobiotic-Metabolizing Enzymes 60

Cytochrome P450 Monooxygenases 60

Flavin-Containing Monooxygenase 63

Other Phase I Enzymes 65

Epoxide Hydrolases 65

Prostaglandin Synthetase 65

Aldehyde Oxidase 65

Hydrolases and Amidases 66

DDT Dehydrochlorinase 66

Phase II Xenobiotic-Metabolizing Enzymes 66

Glutathione S -Transferases 67

Glucuronyl Transferases 68

Sulfotransferases 68

Other Phase II Enzymes 68

Methyltransferases 68

Cysteine Conjugate β -Lyase 69

Acylation 69

Phosphate Conjugation 69

Summary and Conclusions 69

References 69

INTRODUCTION
Williams (1959) first suggested that the metabolism of xenobiotics generally occurs
in two phases. The word xenobiotic, however, was coined later, in the mid-1960s, by
Dr. Howard Mason to serve as a collective noun including any chemical to which an
organism is exposed and which is extrinsic to the normal metabolism of that organ-
ism. Thus it includes pesticides, occupational chemicals, clinical drugs, drugs of abuse,
deployment-related chemicals, etc., and is a particularly useful term when discussing