The Power of Purple

Posted by

Dov Michaeli

First published 5/5/11 on The Doctor Weighs In

So there we were, standing around a squatting Quechua Indian woman in Chinchero, high in the Andes of Peru. They were weavers of Andean Llama, Alpaca and Vicuña textiles, famous for their rich colors and wonderful designs. Where did the pigments come from? We very quickly found out. They made a small heap of gray scale- insects (called cochineal) that they collected from a certain species of cactus growing locally. One of the women crushed it with a pestle, the other poured some lemon juice on it, and we all gasped –the crushed powder turned red, then red-purple, and finally a beautiful blue-purple. I felt the same sense of wonder as I felt in elementary school, when the teacher demonstrated the litmus test. But beyond that, we all felt a sense that we just witnessed a very complicated chemistry carried out by people who are one with their environment, living its most intimate secrets. As members of generation X or Y would say: awesome! How did they stumble on the fact that crushing gray cochineal insects (pronounced Cochi NEEL in the local language), would produce carminic acid and adding thecalcium citrate in lemon juice would render the powder into a living purple pigment (also called carmine blue)? Of course there was no use asking the women. For them chemistry is not a laboratory exercise; it is as obvious as knowing that the sun goes up in the morning and sets it the evening. It is simply part of their universe.

The surprising role of purple in history

As early as 3000 years ago the ancient Phoenicians made three major discoveries. They gave us the alphabet we are using today. They discovered that by heating silicon oxide, found in unlimited quantities in the sands of the Mediterranean beaches, they could make glass. And, by extracting the secretions of the sea shell Bolinus brandaris (also called Murex brandaris) found on the beaches of the eastern Mediterranean they could make a highly-prized purple dye that did not fade with time but rather increased inbrilliance with exposure to air and sunlight. It was called Tyrean Purple, after the Phoenician port city of Tyre. From a closely related species they extracted another dye –Royal Blue. Being seafarers and famous traders, (or infamous, as the Greeks and Romans loved to point out), they sold these pigments, and cloth and silk dyed with them, all around the known ancient world, from Egypt to Mesopotamia and to Greece and Rome. The process of extraction was tedious and inefficient: thousands of Murex shells were required for dying one Roman toga; Hence the high price, and the fabulous profits, and the resentment against the Phoenicians as gougers and thieves. Now we know better: it was simply a matter of supply and demand, and they cornered the market.

Because the stuff was so expensive, only kings and emperors could afford it. They allowed senators to have togas with a stripe of purple. But that’s it; commoners could wear white, or earth tones like brown or green. In fact, they passed sumptuary laws, regulating who can wear what. These laws were ostensibly designed to avoid conspicuous consumption; in reality they fixed the demarcation between the aristocracy and the rest of us (assuming, dear reader, that you are not an aristocrat). As a consequence (not completely unintended), they also limited the demand for these sumptuous dresses –keeping the price more affordable for them. The picture above shows the emperor Justinian in all his purple glory.

After the sack of Constantinople in 1204 by…the crusaders! (who were supposed to liberate Jerusalem, not plunder the capital of the Christian Byzantine Empire) the impoverished Byzantine emperors could not afford the dye anymore. Later, medieval kings and fabulously rich Popes (weren’t they sworn to poverty at the start of their ecclesiastical careers?) adorned themselves with Tyrean purple dresses. The Church also controlled the message by paying its favorite artists de jour quite handsomely to tell the stories of the bible through art. So only the artists close to the trough could afford the brilliant purple dye. And the message? Only the VIPs, such as Jesus, Mary, and some king  merited Tyrean Purple.

And so it went until the 18th century and age of enlightenment, when liberal and democratic ideals swept away the symbols of Church and State hierarchy, and chemistry began producing brilliant pigments affordable by the new middle class.

Pigments in Medicine

With the democratizing effect of chemistry-for-the-masses came another revolution: the Biology Revolution. The microscope allowed scientists to view cells for the first time. The electron microscope allowed them to see the innards of the cell. Pathologists are able to stain tissues, depending on their surface charge, with either a blue dye (hematoxylin) or a red one (eosin). And to increase the staining specificity beyond just surface charges, researchers developed antibodies to specific cell types, like lymphocytes or muscle cells or neurons, and bound them chemically to various dyes. Now they could visualize exactly how the heart muscle is organized, or how one lymphocyte type differs from another, or how neurons are organized in the brain.

But as important as this pigment revolution was, it had a major shortcoming: it showed  the cells as static objects. And in biology nothing is static. Cells move within tissues and all around the body; and inside the cells there is a constant flow of proteins and organelles busily performing their duties. For many years researchers could only speculate what’s happening inside the cell, using clues and speculation. But then a quantum jump occurred in the development of pigments that made tracking of cell components inside the cell possible. The first one was a green fluorescent protein (GFP) obtained from a jellyfish. This discovery spawned such a revolution in cell biology and medicine that its discoverers, Martin Chalfie, Osamu Shimomura, and Roger Y. Tsien were awarded the Nobel Prize in physiology and Medicine in 2008.

Here are some short quotes from the Nobel committee:

“To obtain such knowledge (of the dynamic behavior of cells), new experimental and conceptual tools were required. Now, at the beginning of the 21st century, we are witnessing the rapid development of such tools based on the green fluorescent protein (GFP) from the jellyfish Aequorea victoria, its siblings from other organisms and engineered variants of members of the “GFP family” of proteins.”

“Indeed, no other recent discovery has had such a large impact on how experiments are carried out and interpreted in the biological sciences, as witnessed by the appearance of more than 20,000 publications involving GFP since 1992.”

To close the loop, a paper published in the May 2008 issue of Geneticsannounced the discovery of a new Purple Fluorescent Protein. Now we can track simultaneously many proteins and organelles as they course through the cell; some staining green, some blue, some red, and yes –some staining brilliant, majestic purple, a veritable ballet in dazzling colors.

This was quite a journey for the color purple –from the service of emperors and Popes to the service of all humanity. An exhilarating journey indeed.

Dov Michael MD PhD is a basic researcher who writes at The Doctor Weighs In.

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