Non-microsomal Enzymes
| Home | | Pharmacology |Chapter: Essential pharmacology : Pharmacokinetics; Metabolism Excretion Of Drugs, Kinetics Of Elimination
These are present in the cytoplasm and mitochondria of hepatic cells as well as in other tissues including plasma. The flavoprotein oxidases, esterases, amidases and conjugases are nonmicrosomal. Reactions catalysed are:
NON-MICROSOMAL ENZYMES
These are present in the cytoplasm and mitochondria
of hepatic cells as well as in other tissues including plasma. The flavoprotein
oxidases, esterases, amidases and conjugases are nonmicrosomal. Reactions
catalysed are:
Some oxidations and reductions, many hydrolytic
reactions and all conjugations except glucuronidation.
The nonmicrosomal enzymes are not inducible
but many show genetic polymorphism (acetyl transferase, pseudocholinesterase).
Both microsomal and nonmicrosomal enzymes are
deficient in the newborn, especially premature, making them more susceptible to
many drugs, e.g. chloramphenicol, opioids. This deficit is made up in first few
months, more quickly in case of oxidation and other phase I reactions than in
case of glucuronide and other conjugations taking 3 or more months.
The
amount and kind of drug metabolizing enzymes is controlled genetically and is
also altered by environmental factors. Thus, marked interspecies and
interindividual differences are seen, e.g. cats are deficient in glucuronyl transferase
while dogs are deficient in acetyl transferase. Upto 6fold difference in the
rate of metabolism of a drug among normal human adults may be observed. This is
one of the major causes of individual variation in drug response.
