Natural Resources, 2012, 3, 201-205 http://dx.doi.org/10.4236/nr.2012.34027 Published Online December 2012 (http://www.SciRP.org/journal/nr) 1 Tissue-Specific Isoenzyme Variations in Tilapia Fish, Oreochromis niloticus Mohammed Salem AL-Harbi 1 , Sayed Amin Mohamed Amer 1,2* 1 Department of Biology, Faculty of Science, Taif University, Taif, Saudi Arabia; 2 Department of Zoology, Faculty of Science, Cairo University, Giza, Egypt. Email: * yasser92us@yahoo.com Received September 15 th , 2012; revised October 21 st , 2012; accepted November 7 th , 2012 ABSTRACT Native polyacrylamide gel electrophoresis have been used to analyze malate dehydrogenase (MDH), acid phosphatase (Acph) and peroxidase (Px) isoenzymes in different tissues (liver, kidney, muscle and heart) of the tilapia fish, Oreo- chromis niloticus in order to study the tissue specificity of these isoenzymes. Three, two and one fractions have been recorded respectively for the three isoenzymes in different studied tissues. The MDH-1 and MDH-2 have been ex- pressed only in muscle and heart while MDH-3 has been expressed in all studied tissues. The percentage amount of MDH in general varied significantly between muscle and different studied tissues. With respect to acid phosphatase, the percentage amount of the total enzyme showed significant difference between liver and muscle and that this variation may be due to higher gene activity in liver. Peroxidase isoenzyme was recorded in liver and heart only with significant increase in liver. The kidney was the least among the studied tissues in showing gene expression for the studied isoen- zymes and therefore, liver, heart and muscle tissues are better applicable in studying the isoenzymatic profiles for fish physiology and systematics. Keywords: Oreochromis niloticus; Malate Dehydrogenase; Acid Phosphatase; Peroxidase; Isoenzymes 1. Introduction Tilapiini is a highly diverse tribe with more than 70 spe- cies belonging to the order Perciformes, family Cichlidae [1] to which the commonly called tilapia belongs. Tilapia is a generic term used to designate a group of comer- cially important Cichlid fish, which consists of three gen- era: Oreochromis, Sarotherodon and Tilapia [2]. The Nile tilapia O. niloticus is the most widely farmed spe- cies [3], recognized as one of the most important species in tropical and subtropical aquaculture because of their production potential [4]. Several investigations have been concerned with the characterization of tissue-and organ-specific isoenzyme patterns [5-12] among which little were concerned with fishes. Few studies have concerned with the isoenzyma- tic profiles in the Nile tilapia [4,13]. LDH and MDH isoenzymes are major system found in fishes. They are classified in different groups on the basis of their possession in different tissues or cell organelles [14,15]. Chaudhuri and Krishna [16] studied the tissue specificity and the degree of polymorphism of five en- zyme systems in Labeo rohita from Yamuna namely in liver, muscle, heart and brain tissues. Acid phosphatases often occur in multiple forms dif- fering in molecular sizes [17]. In animals its biological role is not yet clear but it is involved in many biological systems which are linked to energy metabolism, meta- bolic regulation and cellular signal transduction pathways [18]. Peroxidase enzyme (H 2 O 2 donor and consumer) con- tains many isoforms which partake in a variety of meta- bolic functions. In animals, peroxidase enzymes are in- volved in phagocytosis and immune cell function [19,20], cell adhesion [21], antioxidant function [22,23] and the oxidative polymerization of hydroquinones to melanin [24]. The present study aimed to investigate whether the studied isoenzymes differently expressed in the different tissues of the Nile tilapia Oreochromis niloticus culti- vated in the Saudi Arabian farms. 2. Materials and Methods Fish samples were freshly obtained from a fish Farm in Makkah city, immediately taken to the lab. Male samples weighing 241 - 276 g were used. The samples were then autopsied and the organs were taken and stored at –80˚C for further laboratory use. The targeted organs were the liver, the kidney, a muscle and the heart. * Corresponding author. Copyright © 2012 SciRes. NR