ROLE OF MOLYBDENUM IN THE BIOLOGICAL FUNCTION 297 ROLE OF MOLYBDENUM IN THE BIOLOGICAL FUNCTION OF SULFITE OXIDASE AND SULFUR DIOXIDE TOXICITY RABIA GEELANI, SHAJRUL AMIN, MINU BALKHI AND AKBAR MASOOD* Department of Biochemistry, The University of Kashmir, Srinagar 190 006, J&K, India Key words : Sulfite oxidase, Molybdenum, Spinaceae oleraceae, Sulfur dioxide . ABSTRACT Sulfite oxidase catalyses the physiologically vital oxidation of sulfite to sulfate in animals, plants and bacteria. Sulfite oxi- dase isolated from animal sources has been shown to contain molybdenum as cofactor. Tungsten is able to replace molybde- num in Mo-enzymes, forming catalytically inactive (or possess- ing very low activity) analogs. Measurable sulfite oxidase ac- tivity was observed in Spinaceae oleraceae grown under normal environmental conditions in absence of any external stress. The tungsten irrigated plants were apparently healthy, but were more susceptible to aqueous sulfur dioxide toxicity. Such plants showed concentration dependent loss of sulfite oxidase activ- ity. A greater decrease in chlorophyll, amino acid and protein content was observed in these plants on treatment with aque- ous sulfur dioxide. It is found that sulfite oxidase in Spinaceae oleraceae like the animal enzyme is a Mo- enzyme and is is instrumental in counteracting the toxic effects of aqueous sul- fur dioxide in plants. INTRODUCTION Sulfite oxidase is a vital enzyme catalyzing the oxidation of sulfite to sulfate. The terminal reaction in the oxidative degradation of the sulfur containing amino acids cysteine and methionine is catalysed by this mitochondrial en- zyme. It belongs to the molybdenum cofactor (Mo-Co) containing family of enzymes. Jr. of Industrial Pollution Control 23 (2)(2007) pp 297-304 © Enviromedia Printed in India. All rights reserved E-mail: akbar masood [akbar_masood@hotmail.com]