Metal binding and ferritin immunoreactivity in a high molecular weight fraction from rat brain

Immobilized metal affinity beads for ferritin adsorption

A new metal-chelate adsorbent utilizing N-methacryloyl-(L)-cysteine methyl ester (MAC) was prepared as a metal-chelating ligand. MAC was synthesized by using methacryloyl chloride and L-cysteine methyl ester dihydrochloride. Spherical beads with an average diameter of 150-200 microm were produced by suspension polymerization of 2-hydroxyethyl methacrylate (HEMA) and MAC carried out in an aqueous dispersion medium. Then, Fe(3+) ions were chelated directly on the beads. Properties such as specific surface area, specific pore volume and ligand occupation were determined. The specific surface area of the beads was found to be 18.9 m2/g. The total pore volume was 2.8 ml/g and represented a porosity over 52%. The average pore size of the poly(HEMA-MAC) beads was 620 nm. Fe(3+)-chelated beads were used in the adsorption of ferritin from aqueous solutions. Ferritin adsorption increased with increasing ferritin concentration. The maximum ferritin adsorption capacity of the Fe(3+)-chelated poly(HEMA-MAC) beads (Fe(3+) loading 0.81 mmol/g) was found to be 3.7 mg/g at pH 4.0 in acetate buffer. The non-specific ferritin adsorption on the poly(HEMA-MAC) beads were 0.4 mg/g. Adsorption behavior of ferritin could be modelled using both the Langmuir and Freundlich isotherms. Adsorption capacity decreased with increasing ionic strength of the binding buffer. Ferritin molecules could be adsorbed and desorbed five times with these adsorbents without noticeable loss in their ferritin adsorption capacity.

Purification and characterization of a high molecular mass serine carboxypeptidase from Monascus pilosus

Two serine carboxypeptidases, MpiCP-1 and MpiCP-2, were purified to homogeneity from Monascus pilosus IFO 4480. MpiCP-1 is a homodimer with a native molecular mass of 125 kDa composed of two identical subunits of 61 kDa, while MpiCP-2 is a high mass homooligomer with a native molecular mass of 2,263 kDa composed of about 38 identical subunits of 59 kDa. This is unique among carboxypeptidases and distinguishes MpiCP-2 as the largest known carboxypeptidase. The two purified enzymes were both acidic glycoproteins. MpiCP-1 has an isoelectric point of 3.7 and a carbohydrate content of 11%, while for MpiCP-2 these values were 4.0 and 33%, respectively. The optimum pH and temperature were around 4.0 and 50 degrees C for MpiCP-1, and 3.5 and 50 degrees C for MpiCP-2. MpiCP-1 was stable over a broad range of pH between 2.0 and 8.0 at 37 degrees C for 1 h, and up to 55 degrees C for 15 min at pH 6.0, but MpiCP-2 was stable in a narrow range of pH between 5.5 and 6.5, and up to 50 degrees C for 15 min at pH 6.0. Phenylmethylsulfonylfluoride strongly inhibited MpiCP-1 and completely inhibited MpiCP-2, suggesting that they are both serine carboxypeptidases. Of the substrates tested, benzyloxycarbonyl-L: -tyrosyl-L: -glutamic acid (Z-Tyr-Glu) was the best for both enzymes. The Km, Vmax, Kcat and Kcat/Km values of MpiCP-1 for Z-Tyr-Glu at pH 4.0 and 37 degrees C were 1.33 mM, 1.49 mM min(-1), 723 s(-1) and 545 mM(-1) s(-1), and those of MpiCP-2 at pH 3.5 and 37 degrees C were 1.55 mM, 1.54 mM min(-1), 2,039 s(-1) and 1,318 mM(-1) s(-1), respectively.

Investigation of the release of iron from ferritin by naturally occurring antioxidants

Ferritin is the main intracellular iron storage protein. The release of iron from ferritin in the presence of a number of phenolic based compounds of nutritional significance was studied at physiological pH. The release of iron was measured by monitoring the formation of the iron(II)-ferrozine complex. The kinetics of this process were studied in Hepes buffer (pH 7.00), at 37 degrees C. The order of ability to remove iron from ferritin is epigallocatechin>gallic acid methyl ester approximately equal to sinapic acid>ferulic acid. The presence of the oxyradical scavenger urea resulted in a slight inhibition in the release of iron from ferritin by both gallic acid methyl ester and epigallocatechin. The ability of each reagent to release iron is interpreted on the basis of their ability to (a) reduce the bound iron and (b) complex the iron with the oxidised form of the phenol, thus mobilising it from the protein. These studies indicate that some phenolic based compounds that have been epidemiologically associated with a negative effect on iron absorption in man, can individually mobilise and release iron from ferritin under suitable conditions.