illuminating science

Today’s guest post comes from Jenny Riesz, a PhD student in Physics at the University of Queensland. Her research is in the field of biophysics; she studies the biological pigment melanin. Read on to find out more! - Joel

Melanin a dark pigment that colours your hair, eyes and skin. It’s found in a huge range of species, from plants, to bacteria, to mammals. There are many different types, but we’re mostly interesting in those that colour skin – eumelanin and pheomelanin. Eumelanin is very black; squid ink consists mostly of eumelanin, with some protein. If you have dark colouring, you have a lot of eumelanin in your skin and hair. Pheomelanin, on the other hand, is red-yellow (red-heads have a lot more pheomelanin than eumelanin). You can see me in the picture in our ‘wet lab’ with a black melanin sample. This will be diluted down until it is almost transparent for spectroscopic measurements.

Melanin is also found in the inner-ear and brain stem, and no one really knows what it does there. We do know that it does something, because melanin deficiencies have been linked to Parkinson’s disease, and white cats (with low melanin levels) are often deaf.

Melanin acts as a photoprotectant in your skin. This means that it’s very good at absorbing light from the sun and dissipating that energy harmlessly (particularly the most dangerous high energy UV light). What’s really interesting is that some people think that melanin can also become carcinogenic, and actually cause the cancer that it is supposed to protect us against. We’re interested in working out why and how this happens, and eventually, how to prevent melanomas.

To study melanin we do spectroscopic measurements: we shine light of different wavelengths (colours) into a sample of melanin and watch how it interacts (does it fluoresce? How quickly and brightly?). We’ve discovered that melanin does fluoresce a little bit of light, but most of the energy is dissipated as heat – about 99.9%! And it does this very quickly – it only takes about 12 picoseconds (that’s 0.0000000000012 seconds!). We’re still trying to understand how it does this by doing calculations and building theoretical models.

I am also particularly interested in the structure of the melanin molecule. Unlike DNA and many proteins that have well understood structures, melanin is very hard to characterize. We know the basic building blocks that form it, but we really don’t know how they connect together to form the black pigment. Knowing the structure is very important if we want to build models to understand how melanin absorbs and interacts with light. Even though melanin has been studied for decades, it remains a most mysterious molecule!