Colloids and Surfaces B: Biointerfaces 89 (2012) 277–282 Contents lists available at SciVerse ScienceDirect Colloids and Surfaces B: Biointerfaces jou rn al h om epage: www.elsevier.com/locate/colsurfb Short Communication Competitive adsorptions of nitrile hydratase and amidase on polyacrylonitrile and its effect on surface modification Vikash Babu, Bijan Choudhury ∗ Department of Biotechnology, Indian Institute of Technology, Roorkee 247 667, India a r t i c l e i n f o Article history: Received 22 May 2011 Accepted 26 August 2011 Available online 3 September 2011 Keywords: Polyacrylonitrile Nitrile hydratase Amidase Vroman effect Specific adsorption a b s t r a c t In this study, enzymatic surface modification of polyacrylonitrile was studied using nitrile metabolizing enzyme of Amycolatopsis sp. IITR 215. During enzymatic treatment of polyacrylonitrile at pH of 5.8 and 7, it was observed that the conversion of cyano group to carboxylic acid at pH 5.8 was three times higher than at pH 7. This difference in enzymatic treatment efficiency was explained by studying the differences in adsorption profiles of nitrile hydratase and amidase on polyacrylonitrile at pH of 5.8 and 7. Adsorption profiles were determined by monitoring the unbound activities of these two enzymes in the supernatant. From the specific activity profiles of bound nitrile hydratase and amidase it was concluded that more specific binding of nitrile hydratase was observed at pH 5.8 as compared to pH 7. In case of amidase, optimum adsorption was obtained at pH 5.8 within 5 h whereas in case of pH 7 it was obtained within 20 h. Thus at pH 7, sequential adsorption of nitrile hydratase and amidase was observed and this adsorption profile was similar to the Vroman effect reported during plasma protein adsorption at solid–liquid interface. Ideally, specific nitrile hydratase adsorption followed by sequential adsorption of amidase may enhance higher conversion of cyano group to carboxylic acid. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Biotransformation involving enzyme has been an area of inter- est due to its significant commercial and environmental benefits [1]. Surface modifications of synthetic polymers using enzyme have also attracted the attention of polymer scientist [2]. Enzymatic modifications of polymers have many advantages over conven- tional physio-chemical methods. Some of the major advantages of enzymatic method are selectivity of enzyme, mild reaction conditions, reaction limited only to surface, greener method and minimal effects on bulk properties of polymers. Physical methods like plasma treatment, UV irradiation, corona discharge can be used for surface modification of polymers with minimal adverse effects on the environment. Some of the disadvantages of physical meth- ods are operational difficulty in continuous operations, generation of heterogeneous functional groups and difficulty in replications in large scale [3]. Among the various hydrolytic enzymes used for surface mod- ification of polymers, nitrile metabolizing enzymes were utilized for the treatment of nitrile polymers. Nitrile hydratase from Bre- vibacterium imperiale and Corynebactrium nitrophilus was used to convert nitrile groups to amide groups in PAN polymers which ∗ Corresponding author. Tel.: +91 1332 285297. E-mail address: bijanfbs@iitr.ernet.in (B. Choudhury). resulted in increase of hydrophilicity [4]. Similarly, nitrile metab- olizing enzymes of A. tumefaciens BST05 were able to incorporate amide group on PAN and only after prolong treatment, traces of ammonia was detected which confirms the formation of carboxyl group [5]. However, Tauber et al. found that nitrile hydratase and amidase from Rhodococcus rhodochrous NCIMB 11216 were able to partially convert –CN groups of granular PAN (40 kDa) and PAN190 (kDa) to the corresponding acid while nitrile group of acrylic fiber was only hydrolyzed to the amide [6]. Fischer-Colbrie et al. iso- lated Micrococcus luteus BST20 and used for the production of membrane-bound nitrile hydrolyzing enzyme which was able to convert nitrile group of PAN powder to the corresponding acid [7]. They confirmed the formation of carboxylic acid by determining the NH 3 release in the reaction mixture and by solid state NMR of treated polymer. Matama et al. reported the enzymatic conversion of nitrile groups of PAN into the corresponding carboxylic groups by commercially available nitrilase [8]. In all these studies, major attentions were on the characteriza- tion of treated polymers and optimization of reaction conditions. Complexity in enzymatic treatments of polymers arises due to the insoluble nature of substrate. Naturally, enzyme in solution has to adsorb on the polymer surface followed by surface catalysis of functional group on polymer. Thus in case of surface modifica- tion of polymer with enzyme, adsorption of enzyme probably plays an important role. Adsorptions of enzymes on solid support have been reported with respect to their adsorption kinetics, stability 0927-7765/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfb.2011.08.025