Abstract
In the mid-1950s, Bert Lester Vallee and his colleague Marvin Margoshes discovered a molecule referred to today as metallothionein (MT). Meanwhile, MTs have been shown to be common in many biological organisms. Despite their prevalence, however, it remains unclear to date what exactly MTs do and how they contribute to the biological function of an organism or organ. We investigate why biochemical research has not yet been able to pinpoint the function(s) of MTs. We shall systematically examine both the discovery of and recent research on Dr. Vallee’s beloved family of MT proteins utilizing tools from philosophy of science. Our analysis highlights that Vallee’s initial work exhibited features prototypical of a developing research tradition: it was upward-looking, exploratory, and utilized mere interactions. Since the 1960s, MT research has increasingly become intervention- and hypothesis-based while it remained largely upward-looking in character. Whilst there is no reason to think that upward-looking research cannot successfully yield structure-function mappings, it has not yet been successful in the case of MTs. Thus, we suggest it might be time to change track and consider other research strategies looking into the evolution of MTs. Recent studies in mollusks render research in this direction worthy of pursuit.
Highlights
After the Second World War, several scientists have been interested in studying the metabolism of metals, especially iron, zinc, and copper in biological organisms
The name is descriptive in nature. It points to a bond between a metal ion and thionein rather than describing a function of these kinds of proteins per se, as is the case, for example, with the alcohol dehydrogenase (ADH) discovered a couple of years earlier [6]
The blue color reminded him of the inactive copper protein isolated by Mann and Keilin in 1938 from the red blood cells of equine serum, named hemocuprein, an enzyme soon referred to as superoxide dismutase (SOD)
Summary
After the Second World War, several scientists have been interested in studying the metabolism of metals, especially iron, zinc, and copper in biological organisms. It points to a bond between a metal ion and thionein (a cysteine rich apoprotein) rather than describing a function of these kinds of proteins per se, as is the case, for example, with the ADHs discovered a couple of years earlier [6]. Using just the term “metallothionein” as a query found over 18 thousand hits in the literature category and 34 thousand under the protein category Six decades after their initial discovery, after literally thousands of studies describing their structure, biochemical characteristics, and tissue distributions, the biological function(s) of MTs still remains enigmatic [15,16]. We conclude that studying the evolution of MTs offers a research direction worthy of pursuit for understanding MT function(s) in vertebrates and beyond
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