دانلود رایگان ترجمه مقاله فیتاز از Weissella halotolerans: خالص سازی و اثر برخی فلزات (نشریه تیلور و فرانسیس ۲۰۱۷)

فیتاز از باکتری Weissella halotolerans: تخلیص، مشخصات جزئی و اثر برخی فلزات

Phytase from Weissella halotolerans: purification, partial characterisation and the effect of some metals

Abstract

In the study, phytase was purified in three simple steps comprising ammonium sulphate precipitation, anion exchange and gel filtration chromatography from Weissella halotolerans. The enzyme was obtained with a specific activity of 227.73 EU/mg and 6.52% recovery. The molecular mass of the enzyme was determined to be 41.52 kDa. The optimum pH and temperature for the enzyme were 6.0 and 50°C, respectively. Furthermore, the effects of metal ions on the enzyme were investigated. Ag+ , Zn2+, Cr2+ and Fe2+ ions inhibited phytase by 21.86, 25.63, 32.82 and 90.43%, respectively, whereas Co2+, Cu2+, Pb2+, Cd2+ ve Mn2+ ions increased the enzyme activity.

۱ Introduction

Phytic acid (myo-inositol hexakisphosphate) is a common compound of plant-derived foods and constitute 1–۵% of edible cornflakes, pollen, and hazelnut oil and seeds in weight. It is an organic form of phosphorus that constitute 60–۹۰% of the total phosphorus content and plays an anti-nutritive role.[1–۳] Although they are important in many physiological functions, especially in seed germination, phytates are solely considered as anti-nutritive compounds because they bind starch and proteins. Phytases affect protein digestion and interact with proteins, and even inhibit the activity of digestive enzymes. They also have a strong chelating effect on divalent minerals including Ca2+, Mg2+, Zn2+ and Fe2+.[4] Although it is a strong chelator of iron and zinc in herbal foods, as a result of being a mediator for these metals, phytate actually acts as an antioxidant that reduces their free radical forms.[4] The effective degradation of phytic acid is obtained through both enzymatic and non-enzymatic degradation.[5] Enzymatic degradation is obtained by using phytase that was derived from a variety of fungus and bacteria. Non-enzymatic hydrolysis is used during food processing or the physical removal of phytate from phytate-rich plant seeds to reduce the phytate levels in end food products.[6]

Phytase (myo-inositol hexakisphosphate phosphohydrolase E.C. 3.1.3.8) disintegrates the phosphoric monoester bonds in phytic acid and phytate. This results in a series of phosphate ester release from myoinositol; therefore, it gained a quick worldwide acceptance as a food additive and animal feed.[7] In the last two decades, it drew the attention of scientists and entrepreneurs for its nutrition, environmental protection and other biotechnological applications. Phytases have many applications in myo-inositol phosphate preparation. Moreover, they are used as precursors and soil improvers in the semi-synthesis of peroxidases in the paper industry and in plant growth.[2] In addition, along with their applications in aquaculture, [8–۱۰] they have important applications in human nutrition; [11] hence, phytases are widely used as food and feed additives and are used to reduce phosphorus pollution in animal feed.[12]

Bacterial phytases have a significant advantage over fungal phytases thanks to their high temperature stability, phytate substrate specifity, resistance to proteolysis and wide pH profile; thus, the purification and characterisation of phytases, which have thermostability and are active at neutral pH, are important in industrial applications. In the study, phytase was purified from lactic acid bacteria, Weissella halotolerans, in three steps comprising ammonium sulphate precipitation, Q-Sepharose anion exchange chromatography and Sephadex G-100 gel filtration column. The characteristic properties of the enzyme were determined and the effects of metal ions on the enzyme activity were investigated.