Riboflavin-binding sites in the flagella of Euglena gracilis and Astasia longa

Abstract

Te photoreceptor for phototaxis in Euglena gracilis is thought to be localized at the base of the major flagellum. Flagella were isolated from Euglena gracilis and from the closely related Astasia longa. In the case of Euglena the paraflagellar body (PFB) remains attached to the flagellum, while the colourless Astasia does not possess a PFB and does not show phototaxis. For comparison, Euglena flagella were obtained without PFBs by an alternative isolation procedure after a cold treatment at pH 4.5. Since various lines of evidence indicate the involvement of a flavin as a possible photoreceptor pigment for phototaxis, riboflavin binding was compared between the flagellar samples. Using [ 3H]-labelled riboflavin, high and saturable binding activity was found in Euglena flagella both with and without PFBs, while Astasia flagella showed hardly any binding activity. The flagellar preparations were analysed by sodium dodecyl sulphate (SDS) gel electrophoresis.