In the early days of biochemistry, the old scientific craving to simplify, to unify, to jam every part of the universe into the same neat model, was still alive and kicking. Aristotle had his Four Elements; Hippocrates his humours; countless thinkers from Plato to Copernicus succumbed to the clean, aesthetically pleasing celestial sphere model of the Solar System. (Bonus points, naturally, if your hypothesis fit nicely with whatever church happened to be dominant in that age.)
In the nineteenth century, the Dutch biochemist Gerardus Johannes Mulder joined this slightly dubious club. His studies began with silk, then extended to egg white, human blood, gelatin, and various materials extracted from plants. Separating out the substances that today we would recognise as proteins, then experimenting with the addition of acid and alkali, Mulder began to detect what looked like an uncanny regularity in these compounds. Since all proteins are made from the same handful of amino acids, this is perhaps unsurprising. Unfortunately, the discovery of the connection between proteins and amino acids was a few decades away, and Mulder drew another conclusion – namely that all of these substances were made up from different numbers of a single basic molecular unit, plus the occasional dash of sulfur or phosphorus.
“…a substance common to all that we designate protein from πρωτεῖος, primarius, which is combined with sulfur and phosphorus in egg white and fibrin … This is the foodstuff of the whole animal kingdom.” (Over Proteine en hare Verbindingen en Ontledingsproducten, 1838)
One compound present throughout the animal kingdom, and the plant kingdom too, in every part of every organism’s body, manufacturing every substance you could conceivably need just by joining together in different ratios. Simplicity and universality, check and check. The chemist Berzelius’ suggestion that Mulder name it protein, ‘primary’, ‘of the first rank’, must have seemed supremely fitting back in the 1800s. Who could possibly grudge a substance like that its position as the crown jewel of biochemistry?
In the years to come, the chemist Liebig would continue the Aristotelian theme by proposing that there were only four fundamental proteins in nature (albumin, fibrin, casein and gelatin – egg white, blood clots, a milk protein, and the jelly-like substance produced by partially breaking down collagen, the main constituent of skin and muscle). The last analysis of the human proteome put the number of different proteins in the human body at around 19000, so it’s safe to say this hypothesis needed a little work.
And, just to top it all off, in the 20th century a little substance known as DNA began to look a lot more interesting. Speculation about how traits were inherited led to research that would eventually conclude that all proteins were in fact made using a set of specifications contained in DNA. To make matters worse, current thinking suggests life on Earth may have at first been composed entirely of RNA – with this single-stranded cousin of DNA serving both as the blueprint to make biological molecules, like its double-helix’d relative, and the building blocks for the molecules themselves, as proteins do today. Poor Mulder. Proteins weren’t the first; they probably weren’t even the second.
- Bradford Vickery, H., 1950. The Origin of the Word Protein, Yale Journal of Biology and Medicine.
- Foltmann, B., 1980. Protein Sequencing: Past and Present, Biochemical Education.
- Fang, J., 2014. First Complete Mapping Of Human Proteome Discovers 193 New Proteins, iflscience.com.
- Charles Scribner’s Sons, 2008. Mulder, Gerardus Johannes, Complete Dictionary of Scientific Biography.