Suppose Dripping Springs Med Spa were a mineral spring

Removing metals, then adding them back

In a cell-based experiment published in 1982, removing metals from serum thymic factor abolished its biological activity in the rosette assay. Zinc salts restored activity. Other metals did so to a lesser extent, and a 1:1 metal-to-peptide molar ratio gave optimal activation. The authors proposed the name thymulin for the zinc-bound active form.

The substitution gives me real pleasure. An ingredient disappeared, a measured activity disappeared with it, and the replacements performed differently. Calling the ingredient a mineral would have left the most interesting distinction unresolved. Zinc earned its particular place in this experiment.

The spring in the name prompts a curiosity about composition before any grand claim about renewal. Its water is an image, not a treatment proposition. The actual subject is a thymic peptide whose activity changed when its metal partner changed.

The ratio and the assay

The metal-removal experiment measured biological activity with a cell-based test. Its optimal ratio describes the preparation in that test; it supplies no human treatment instructions. I favour testing different metals over the comforting adjective mineral-rich. Here, a loose enthusiasm for minerals has to answer to the metal, the peptide and the assay.

There is a second pleasure in this story: the apparently small ingredient makes the name of the active form meaningful. The later zinc–thymulin review describes a zinc-dependent peptide with a specific three-dimensional conformation. Chemistry has given the spring metaphor a useful limit. The question concerns a particular molecular partnership.

Beyond the preparation

The metal test stays close to removal, replacement and proportion. The human zinc study moves into adults with mild zinc deficiency, where plasma zinc and thymulin activity gave different impressions. Research in old mice and isolated thymus cultures changes the setting again.

Those changes of setting matter to the argument. I admire the discrimination between the replacement metals. How much of that specificity survives the journey into a whole organism interests me increasingly. Each setting adds something that the attractive picture of a mineral spring leaves out.