Subcellular distribution of okadaic acid in the digestive gland of Mytilus galloprovincialis: First evidences of lipoprotein binding to okadaic acid

The subcellular distribution of okadaic acid, the main diarrhetic shellfish poisoning (DSP) toxin, in the cells of the digestive gland of the mussel Mytilus galloprovincialis was studied. By means of differential centrifugation, ultrafiltration and extraction with methanol, it was found that most okadaic acid was stored in the cytosol. Notwithstanding only a small proportion of the total toxin was found to be in free form, being most of it bound to a soluble cellular compound with a molecular mass which ranged from 30 to 300 kDa. A series of fractionations of samples digested with a protease, a lipase, and amylase suggested that the component to which okadaic acid is bound is a high density lipoprotein. A new fractionation after digestion with a protein lipase additionally supports the previous conclusion.