Extended Abstracts / Chemico-Biological Interactions 157–158 (2005) 353–434 375 patients showed significantly greater mean waist-hip ratio (0.97 ± 0.01) than UU patients (0.93 ± 0.01); (3) The K allele frequency (22.0%) in patients with metabolic syndrome (MS) is higher than in patients with- out MS (11.2%; P = 0.027). The association of the K allele and DM1 of earlier onset is reinforced by pre- vious relation of low butyrylcholinesterase activity and immune dysfunction. The K allele in DM2 may predis- pose to a higher risk of MS. (Supported by CNPq and CAPES). Reference [1] Y. Hashim, D. Shepherd, S. Wiltshire, R.R. Holman, J.C. Levy, A. Clark, C.A. Cull, Butyrylcholinesterase K variant on chromosome 3q is associated with Type II diabetes in White Caucasian subjects, Diabetologia 44 (2001) 2227–2230. doi:10.1016/j.cbi.2005.10.060 (16) The effects of indole-3-acetic acid on human and horse serum butyrylcholinesterase Ebru Bodur ∗ , A. Nese Cokugras Hacettepe University, Faculty of Medicine, Department of Biochemistry, 06100 Ankara, Turkey Abstract Butyrylcholinesterase (BChE) constitutes the first line defense in the serum of higher organisms and is a marker for toxic exposure. Indole-3-acetic acid (IAA) is a major plant growth hormone of the auxin class, affecting cell enlargement, and differentiation. As a result of the indus- trial usage, this agrochemical is consumed by non-target organisms. In this study, the interaction of IAA with purified human and horse serum BChEs were investi- gated. Both BChE species displayed biphasic hill plots using butyrylthiocholine as substrate. IAA interaction with BChE species was stable and concentration depen- dent. IAA was found to be linear-mixed type inhibitor for human serum BChE, and alpha and the K i values were 2.15 ± 1.09 mM and 3.09 ± 0.95 mM, respectively. With horse enzyme IAA displayed uncompetitive inhi- bition with the K i value of 1.05 ± 0.09 mM. Acquisition of large amounts of IAA is unlikely but it can be taken as a basis for future inhibitor designs. Keywords: Butyrylcholinesterase; Human; Horse; Serum; Indole-3-acetic acid; Hill plot 1. Introduction Serum BChE constitutes one of the main detoxifi- cation agents because of its abundance and ability to hydrolyze a wide variety of esters [1]. Indole acetic acid (IAA) is a major plant growth hormone of the auxin class, affecting cell enlargement, division, and differen- tiation [2]. It is metabolized by two different pathways; conjugation with a variety of amino acids, peptides, and sugars forming non-reactive conjugates and, oxi- dation by peroxidases leading to produce a toxic series of intermediates which could be used as the basis of a novel cancer therapy [3]. The profusion of BChE in a range of tissues linked with detoxification like kid- neys, lungs, intestine and the presence of its sialogly- cated forms in serum confer them to be perfect bioscav- engers [4,5]. BChE is a peculiar enzyme displaying non-Michaelis–Menten kinetics [6,7]. We investigated the kinetic interactions of IAA with human and equine BChE. The kinetic behavior and the interaction of IAA with both BChE species was assayed using butyrylth- iocholine as substrate. The human and horse enzymes differ from each other most distinctly in the active site structure, an extra negative charge in the omega loop ren- ders the horse enzyme effectively in to a triple human mutant (A277V/G283D/P285L) [8]. Designing specific ChE inhibitors is important for neurodegenerative dis- eases like Alzheimer’s disease. The investigation of inhibitory effects of natural compounds on ChEs forms an alternative approach to such new drug design. 2. Materials and methods 2.1. Materials and enzymes Butyrylthiocholine iodide (BTCh), 5-5 ′ -dithiobis (2- nitrobenzoic acid) (DTNB), 3-(N-morpholino) propane- sulfonic acid (MOPS) were from Sigma (USA), and indole-3-acetic acid (IAA) from BDH. All other chemi- cals used were of the best analytical grade. Human serum butyrylcholinesterase was purified as previously [6]. Horse serum BChE (eqBChE) was puri- fied according to the method of Lockridge and La Du [9]. The overall purification was 6000-fold. Protein concen- trations of the pure enzymes were calculated from their absorbance at 280 nm, using the extinction coefficient 1.8 cm -1 [9]. ∗ Corresponding author. Tel.: +90 312 3245885; fax: +90 312 3110588. E-mail address: bodurebru@yahoo.com (E. Bodur).