Effects of perturbants on the pink (reduced) active form of uteroferrin. Phosphate-induced anaerobic oxidation

Interaction of anions with rat liver arginase: specific inhibitory effects of fluoride

The inhibitory effects of anions, such as N(3)(-), NO(2)(-), BO(4)(3-), SCN(-), CH(3)COO(-), SO(4)(2-), ClO(4)(-), H(2)PO(4)(-), CN(-), I(-), Br(-), Cl(-) and F(-), on the hydrolysis of L-arginine (L-Arg) by rat liver arginase (RLA) have been studied. From all these anions, only F(-) exhibited a clear inhibitory effect at the mM level. Inhibition of RLA by F(-) is reversible and uncompetitive towards L-Arg binding with a K(i) value of 1.3+/-0.5 mM at pH 7.4. This effect is dependent on pH as the IC(50) value of F(-) towards RLA increases from 1.2 to 19 mM when increasing the pH from 7 to 10. Another specific inhibitor of RLA, N(omega)-hydroxy-L-nor-arginine (nor-NOHA), that has been recently shown to bind to RLA as a bridging ligand of its (Mn(II))(2) cluster, exhibits some similarities with F(-) in its inhibitory effects (identical pH dependence). It is thus tempting to propose that the inhibitory effects of F(-) could be due to its binding as a bridging ligand of the RLA (Mn(II))(2) cluster. However, further studies are required to determine the modes of interaction of F(-) with RLA.

Histochemical investigations on the localization of the purple acid phosphatase in the bovine spleen

The localization of the purple tartrate-resistant, iron-containing acid phosphatase in the bovine spleen was studied by enzyme histochemistry at the light and electron microscopic levels as well as by immunohistochemistry. The purple phosphatase was localized only in lysosome-like-organelles of cells belonging to the reticulo-phagocytic system. The same cells were identified as containing large iron(III)-deposits as ferritin in homogeneously granular accumulations and freely in the cytoplasm, or as hemosiderin in siderosomes. The phagocytosing cells containing purple phosphatase and ferritin often had close contact with clusters of aged and deformed erythrocytes. A possible catabolic role of the purple enzyme as a phosphatase degrading phosphoproteins of the erythrocyte membrane and the cytoskeleton was assumed.

The interaction of phosphate with the purple acid phosphatase from beef spleen: evidence that phosphate binding is accompanied by oxidation of the iron chromophore

Reaction of the reduced (pink) form of the purple acid phosphatase from beef spleen with excess phosphate at pH 5.0, monitored by optical and low temperature EPR spectroscopy and by measurement of enzymatic activity, results in parallel loss of activity and oxidation of the iron chromophore. Colorimetric and radiochemical (32P) experiments indicate the presence of one mole of tightly bound phosphate in the oxidized (purple) form of the enzyme; this phosphate is released upon reduction. Acid hydrolysis of 32P-phosphate-containing enzyme, followed by high voltage paper electrophoresis, gave no evidence for significant amounts of acid-stable phosphoamino acids.