Localization of Sepiapterin Deaminase and Pteridines In the Granules In Epidermal Cells of the Silkworm, Bombyx mori

Abstract

A new method for assay of sepiapterin deaminase (3.5.4.24) activity by use of high performance liquid chromatography (HPLC) was developed. By this sensitive method the enzyme activity in the cell organelle was assayed. After cell fractionation, the enzyme was extracted with deoxycholate from pteridine granules of epidermal cells of the lemon mutant silkworm. On stepwise sucrose gradient centrifugation, most of the enzyme activity localized in the aggregated pteridine granules fraction, while the soluble fraction contained only one fourth of the total enzyme activity. The enzyme in the granule fraction had the same properties as the previously reported sepiapterin deaminase. These data show that the enzyme is localized in pteridine granules in the living cells. The attachment of the enzyme to the granule membrane is rather loose and previous papers studied the enzyme released from the granules. Cell fractionation and morphological observation showed that sepiapterin, sepialumazine and other pteridines were also localized in the granules together with uric acid.