Edited by Miguel De la Rosa Keywords:Purple acid phosphatase Diphosphonucleotide phosphatase Phosphodiesterase PPD Fe-Mn center a b s t r a c t Yellow lupin diphosphonucleotide phosphatase/phosphodiesterase (PPD1) represents a novel group of enzymes. Here we report that it possesses one iron atom and one manganese atom (1:1 molar ratio) per subunit. The enzyme exhibits visible absorption maximum at $530 nm. Prolonged oxidation of PPD1 leads to loss of the charge-transfer band and catalytic activity, whereas after reduction PPD1 remains active. Replacement of conserved amino-acid residues coordinating metals results in the loss of enzymatic activity. Despite low amino-acid sequence homology of PPD1 to well-characterized $55-kDa purple acid phosphatases, their overall fold, topology of active center and metal content are highly similar.

The expressions of terminal sugars in synovial and plasma fibronectins were studied in relation to rheumatoid arthritis (RA) progression defined according to the early, established and late radiological changes in the patients' hands. The relative amounts of sialic acid and fucose were analyzed by lectin-ELISA using appropriate sialic acid-linked alpha2-3 (Maackia amurensis) and alpha2-6 (Sambucus nigra) lectins as well as fucose-linked alpha1-6 (Aleuria aurantia), alpha1-2 (Ulex europaeus), and alpha1-3 (Tetragonolobus purpureus). In the early RA group, the synovial fibronectin reactivities were the lowest with the all lectins used. In the established and late groups, relative sialylation and fucosylation significantly increased. However, sialylation negligibly decreased, whereas fucosylation remained at nearly the same level in the late group. Moreover, the expression of alpha1-6-linked fucose was found to be related to disease activity. In contrast, plasma fibronectin reactivity with lectins showed different dynamic alterations. In the early RA group, the reactivity of fibronectin with the lectins used was similar to that of healthy individuals, whereas it increased significantly in the established RA group compared with the early and normal plasma groups. In the late RA group it decreased to a level similar to that of the normal group. The lower expressions of terminal sugars in synovial fibronectin were mainly associated with the early degenerative processes of RA. In conclusion, such alterations may be applicable as a stage-specific marker for diagnosis and therapy of RA patients. The higher expression of terminal sugars in fibronectin could be associated with repair and adaptation processes in longstanding disease.