ROLE OF MOLYBDENUM IN THE BIOLOGICAL FUNCTION OF SULFITE OXIDASE AND SULFUR DIOXIDE TOXICITY
Sulfite oxidase catalyses the physiologically vital oxidation of sulfite to sulfate in animals, plants and bacteria. Sulfite oxidase isolated from animal sources has been shown to contain molybdenum as cofactor. Tungsten is able to replace molybdenum in Mo-enzymes, forming catalytically inactive (or possessing very low activity) analogs. Measurable sulfite oxidase activity 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 activity. A greater decrease in chlorophyll, amino acid and protein content was observed in these plants on treatment with aqueous 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 sulfur dioxide in plants.
RABIA GEELANI, SHAJRUL AMIN, MINU BALKHI AND AKBAR MASOOD
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