The Science of Melanin

Watch

1. The Science of Melanin Magicyoutube.com/watch?v=5Dt1NYLqMqM

Word of the day

Melanin (MEL-uh-nin). A family of pigments in living things. Cells make eumelanin and pheomelanin from the amino acid tyrosine.

• Melancholy, a word for deep sadness, comes from Greek melancholía, “condition of having black bile.”
• Keratin, the protein that makes up hair and nails, carries the same -in ending as melanin.

Bonus words. Eumelanin (yoo-MEL-uh-nin, from eu-, “good”) names the brown to black melanin. Pheomelanin (fee-oh-MEL-uh-nin, from pheo-, “gray”) names the red to yellow melanin, which contains sulfur.

Predict

1. Red hair holds a lot of pheomelanin. Chemists track pheomelanin with TTCA, a marker molecule that comes from pheomelanin when hair is broken down. Before you read the paper, take a guess. Black hair holds what percent of red hair’s TTCA? Give your reason in one sentence.

   Hint. Think about which kind of melanin the video says colors black hair.

Read the paper

Ito and others, “Improved HPLC Conditions to Determine Eumelanin and Pheomelanin Contents in Biological Samples Using an Ion Pair Reagent,” International Journal of Molecular Sciences, 2020. The paper is free to read.

Chemists measure melanin by breaking the pigment into small marker molecules and measuring the markers. Alkaline hydrogen peroxide breaks eumelanin into PTCA, PDCA and PTeCA, and breaks pheomelanin into TTCA and TDCA. The markers show how much of each melanin a sample holds and what its building blocks look like. Table 2 of the paper reports all five markers in one sample of black human hair and one sample of red human hair, from five repeat analyses. Values are means ± standard deviation, in nanograms of marker per milligram of hair. The coefficient of variation (CV) sits in parentheses. PTCA, PDCA and PTeCA come from eumelanin. TTCA and TDCA come from pheomelanin.

1. For each hair color, fill in the last column of the table by dividing TTCA by PTCA. How many times higher is red hair’s TTCA-to-PTCA ratio than black hair’s ratio? And what percent of red hair’s TTCA does black hair hold?

   Hint. Find both ratios first. For the percent, divide black hair’s TTCA by red hair’s TTCA.

2. TTCA and TDCA are thiazoles, rings that hold a sulfur atom (thiazole is C3H3NS). PTCA, PDCA and PTeCA are pyrroles, rings with no sulfur (pyrrole is C4H5N). Pheomelanin forms when the amino acid cysteine (C3H7NO2S) joins dopaquinone, which tyrosinase makes from tyrosine (C9H11NO3). Black hair yielded 43.4 nanograms of TTCA per milligram. What does that TTCA tell you about cysteine inside the melanocytes that colored black hair?

   Hint. Trace the sulfur atom. Which starting molecule could have supplied the sulfur?

3. Table 2 gives each value as mean ± standard deviation from five repeat analyses, with the CV in parentheses. Most CVs fall under 5%, but PTeCA in red hair reached 12.4% and TDCA in black hair reached 9.7%. Why would PTeCA in red hair and TDCA in black hair vary more than the other markers? And why run the same hair sample five times?

   Hint. Look at how much of each marker the hair holds. Then look at Table 1 of the paper, where a smaller slope means a smaller detector signal for the same amount of marker.

4. Eumelanin absorbs UV and soaks up harmful oxidants. Pheomelanin blocks less UV and can produce reactive oxygen species when UV hits the pigment. People whose MC1R works weakly often have red hair and fair skin. Based on Table 2, which would likely give skin less protection from UV, melanocytes like the red-hair ones or the black-hair ones? And what would you measure in skin to test that prediction?

   Hint. Hair isn’t skin. Think about which samples and which kind of damage you would measure.

Exit ticket