Extraction and charaterization of tyrosinase from peanut grownin north of Iran

Formation of brownish yellow pigments in damaged fruits and vegetables by tyrosinase enzyme is one of the main causes of their quality loss. Tyrosinase is a metaloprotein and is used in researches, regarding food, pharmacology and cosmetics. Peanut is one of the most important strategic agricultural products of northern Iran. In a general survey from the local farmers and producers, it was found that many of older peanuts lose their market and are reduced in quality and price when the new crop product is entered into the market. Considering the experience and the experties within our group on tyrosinase extraction and characterization, the aim of this research was focused on peanut tyrosinase. Peanut was grounded in liquid nitrogen, followed by precipitation by ammonium sulphate and dialysis. Electrophoresis showed the presence of two possible isozymes. Enzyme activity was determined during various stages of purification. Some important physical properties of the enzymes were also measured. It was shown that the optimum pH for peanut tyrosinase was 5.2 and that optimum temperature was 40 ºC. Kinetics studies determined the Michaelis-Menton constants, i.e. Km= 257.5 mmol and Vmax= 0.00421 mmol/min. The ultimate goal of this research was to investigate the possibility of replacing peanut tyrosinase for mushroom tyrosinase in various industrial and research applications.