Metal-binding ligands in Viokase.

The object of this study was to detect low molecular weight zinc binders in Viokase, a porcine pancreatic preparation used in the treatment of variant acrodermatitis enteropathica (AE). Extracts were centrifuged and ultrafiltered to yield a soluble fraction containing solutes of molecular weights less than or equal to 500 daltons. These were studied by modified gel chromatography (MGC) using sealed Sephadex G-15-120 columns equilibrated with buffered solvent systems containing either 5 ppm copper (II) or 5 ppm zinc (II). Eluted fractions were assayed for these metals by atomic absorption and for amino acids by various techniques. MGC profiles of ultrafiltrates resulted in a peak consisting of glutamic acid and another peak consisting of several amino acids. A third peak was due to metal ions. Citrate and picolinate have been claimed to be important zinc-binding ligands in Viokase, but neither was detectable by MGC, although small amounts of citrate or similar compounds were detected by the Furth and Herrmann reaction. Since amino acid ligands are easily detectable by MGC, and metal distribution among ligands is competitive in nature, the possibility of a role for citrate or picolinate as a zinc transporter in Viokase is seriously reduced. Relief to the variant AE patient was probably not due to citrate- or picolinate-enhanced zinc uptake.