1022-7954/04/4011- © 2004
Russian Journal of Genetics, Vol. 40, No. 11, 2004, pp. 1215–1222. From Genetika, Vol. 40, No. 11, 2004, pp. 1475–1482.
Original English Text Copyright © 2004 by Ta kin, Kence.s
Organophosphate (OP) esters are being used as pes-
ticides and chemical warfare agents. These are very
toxic chemicals since one molecule of OP inhibits one
molecule of acetylcholinesterase enzyme (AChE) at the
active site serine residue which cause muscle paralysis
and seizures and may lead to death of the organism .
OP insecticides have been used from the beginning of
(sheep blowfly) and
(housefly). The first OP resistant insects
were determined at mid 1960s and have risen to a high
frequency [2, 3].
Malathion [S-(1,2-dicarboethoxyethyl) O,O-dime-
thyldithiophosphate)] is one of the most frequently
used OP because of its low acute toxicity compared to
other OP insecticides. It is an exceptional OP by con-
taining two carboxylester groups and phosphotriester
moiety that define it as an OP. Malathion preparations
contain traces of several oxon OPs and it is activated
in vivo to malaoxon by mixed function oxidases. Acti-
vated oxon forms of OPs including malaoxon are pow-
erful inhibitors of malathion carboxylesterase (MCE)
and AChE activities .
In aphid (
) and mosqitoes (
) resistance to OPs is
achived by tandem gene amplifications of up to 300
copies of a particular carboxylesterase gene (nearly 3%
of the total protein of the organism). Even though, the
enzyme has negligible OP hydrolytic activity, overex-
pression enables it to sequester sufficient amount of
OPs for the organism to survive, which prevents the in-
hibition of target site AChE [2, 5, 6].
strains resistance to
diazinon and malathion is mainly caused by a carboxy-
lesterase gene on the fourth and second chromosomes,
respectively . This major OP resistance gene (in
) encodes the major ali-esterases of
which are also known as esterase
isozymes, ALI and E3, respectively [8, 9]. The
genes are located in a cluster of closely re-
lated esterase genes, called
-esterase cluster .
genes were isolated, cloned
and expressed in vitro, and a Gly
was found in the active site of the enzyme from diazi-
[11, 12]. A different amino acid substitutions Trp
Leu were found in the
gene in malathion resis-
strains [3, 9].
Products of both alleles can detoxify a broad and
overlapping range of oxon OPs. The resistance in these
two types are associated with OP hydrolase activity
(defined as the hydrolysis at phosphotriester moiety of
the insecticides) and low ali-esterase activity (defined
as the hydrolysis of aliphatic esters such as methyl bu-
tyrate) [3, 4, 9]. This led to a proposal that each type of
OP resistance in these organisms is the result of a mu-
tation in a specific carboxylesterase that enhanced the
enzyme’s turnover rate of certain OP compounds but at
the same time compromised the enzyme’s activity to-
ward artificial ester substrates (the “mutant ali-esterase
hypothesis”) [3, 9, 12, 13].
The Genetic Basis of Malathion Resistance in Housefly
L.) Strains From Turkey*
V. Ta kin
Department of Biology, Mugla University, Mugla, Turkey;
fax: (+90) 252-224-86-56; e-mail: email@example.com, firstname.lastname@example.org
Department of Biology, Middle East Technical University, Ankara, Turkey
Received October 31, 2003
—Organophosphate insecticide (parathion/diazinon) resistance in houseﬂy (
L.) is associ-
ated with the change in carboxylesterase activity. The product of
gene is probably playing a role in detoxiﬁ-
cation of xenobiotic esters. In our research, we have isolated, cloned and sequenced the
gene from ﬁve dif-
ferent Turkish houseﬂy strains. High doses of malathion (600
g/ﬂy) were applied in a laboratory environment for
one year to Ceyhan1, Ceyhan2, Adana, and Ankara strains while no insecticide treatment was performed in the lab-
oratory to Kirazli strain.
substitution was found in the product of
gene in all malathion-resis-
tant and Kirazli stocks. In addition, we checked the malathion carboxylesterase (MCE), percent remaining activities
in acetylcholinesterase (AChE), glutathion-S-transferase (GST), and general esterase activities in all ﬁve strains used
in this study. In comparing with universal standard sensitive control WHO, a high level of MCE and GST activities
were observed while lower level of general esterase activities was detected in the tested strains. In addition, a higher
percent remaining activities in AChE than WHO susceptible strain were observed in all malathion-resistant strains.
* This article was submitted by the authors in English.