Study of the conversion of GDP‐mannose into GDP‐fucose in Nereids: a biochemical marker of oocyte maturation

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Abstract
Homogenates of Perinereis cultrifera oocytes were found to transform GDP‐d‐mannose into another sugar nucleotide. Ultraviolet absorption spectra, chromatographic behaviour, gas‐liquid chromatography coupled to mass spectrometry analysis revealed that GDP‐d‐mannose had been converted into GDP‐l‐fucose. This conversion is a multi‐step reaction as proved by the involvement of two intermediates identified as GDP‐4‐oxo‐6‐deoxy‐d‐mannose and GDP‐4‐oxo‐6‐deoxy‐l‐galactose, this latter being reduced by NADPH to give GDP‐l‐fucose. It is shown that the enzymatic activities responsible for the conversion of GDP‐d‐mannose into GDP‐l‐fucose is recovered only in oocytes and is not present in the other coelomic cells (i.e. coelomocytes). More interesting is the fact that maximum‐activity is recovered at a well defined stage of the hormone‐controlled oogenesis. Thus, this enzymatic system appears as a biochemical marker of the oocyte maturation in P. cultrifera.