Mol Of Copper Research Articles

The determination of cuprous ion in copper proteins

The reagent 2,2′-biquinoline in glacial acetic acid has been used by a number of workers to measure cuprous-ion concentration in copper proteins. It is shown that the use of this reagent with Limulus hemocyanin gives incorrect results because of the presence of sulfhydryl groups in the protein which are capable of reducing cupric ion. The addition of three moles of p-mercuribenzoate per mole of copper is just sufficient to prevent this reduction. It is also possible to avoid reduction of cupric ion by modification of the biquinoline reagent with ethylenediaminetetraacetic acid. The modified method is generally applicable to the measurement of protein-bound cuprous ion in the presence of reducing groups or molecules.

Apparent ionization constants, spectral properties and metal chelation of the cotransaminases and related compounds

1. 1. The apparent ionization constants of pyridoxal, pyridoxine, pyridoxamine, pyridoxal 5-phosphate, and pyridoxamine 5-phosphate have been determined. 2. 2. The compounds exist as zwitterions in neutral solution. 3. 3. The acid strength of the phenolic hydroxyl group follows the order pyridoxamine > pyridoxamine phosphate > pyridoxal phosphate > pyridoxal > pyridoxine. 4. 4. The base strength of the heterocyclic nitrogen atom follows the inverse sequence pyridoxine > pyridoxal > pyridoxal phosphate > pyridoxamine phosphate > pyridoxamine. 5. 5. The effect of ionization of the phenolic hydroxyl group and ring nitrogen atom on the ultraviolet absorption spectra have been recorded systematically. 6. 6. Titration of pyridoxal in the presence of excess ethanolamine, ethylalanate, or ethylenediamine gave a new partial equivalent of acid consumed in the pH range 5.0–6.5. This new partial equivalent probably represents the titration of a Schiff base derivative of the amines with pyridoxal. 7. 7. Titration of pyridoxamine in the presence of various metals showed that only copper, of the series tested, efficiently chelated with the vitamin in neutral solution. 8. 8. The emerald-green copper chelate of pyridoxamine contains two moles of pyridoxamine per mole of copper. Both the phenolic and amino groups of pyridoxamine enter into chelate formation with the metal.