How The Concept of Banana Browning Links In With Parkinson's Disease

What causes a banana to turn brown, and how does that directly affect our brain functions?

The banana is a carbolicious fruit that many of us do enjoy snacking on. It’s a source of quick, “natural” energy. Professional athletes chomp down on them in between games to get their second wind.

We love using it in other carby dishes, such as with ice cream (the banana split), pancakes, waffles or with bread.

In fact, people who grew up in the UK in the 1980s and the 1990s would also have been exposed to little Eric Wimp, a wimpy looking kid who gains superhuman strength after eating a banana — and becoming Bananaman in the process.

But of course, I’m not here to wax lyrical on Bananaman.

Rather, I’d be looking at what our human body has in common with the banana. See the brown spots in the image? That’s what I’ll be discussing here.

What are those brown spots, exactly?

According to this article,

The dark spots on fruits such as bananas can be attributed to the presence of melanin.

Now, hang on a second. We do have melanin in our bodies too. In fact, the melanocyte cells in our bodies are responsible for producing this melanin, and the melanin that we have in our hair determines whether our hair has colour or not. A lack of melanin in the hair would be a good indicator that our hair would be greying or silvery:

The mechanism behind the formation of those melanin spots

The major controller behind the rate of melanin synthesis is the tyrosinase enzyme. Tyrosinase is an enzyme that oxidises the amino acid tyrosine (which we can find in the proteins that we consume).

As it is written in this article, tyrosine is oxidised by tyrosinase to 3,4-dihydroxyphenylalanine (DOPA) to dopamine, which is then eventually converted into eumelanin, which is the most common type of melanin pigment occurring in humans. This sequence of biochemical reactions is known as the Raper-Mason pathway.

In the banana, any aging or damage sustained to the fruit triggers the activity of tyrosinase to convert tyrosine into melanin too. Hence, whole bananas “are prone to rapid browning during handling, peeling and slicing operations and even storage, if ripening is not adequately controlled”, because of the damage that they are sustaining during all the handling operations that are involved.

But what are the deeper implications of tyrosinase and melanin in our body?

An improper regulation of tyrosinase enzyme activity can result in the development of melanomas, or skin cancer. The abnormal browning of the skin from the overproduction in melanomas can be attributed to an abnormal tyrosinase activity.

We also did briefly touch on the conversion process of tyrosine to DOPA to dopamine. Dopamine is an important neurotransmitter that is released in the brain after a feelgood meal has been consumed.

Much like a lack of serotonin production can cause issues with mental health, a lack of dopamine production in the brain can also contribute to a lack of motivation and symptoms of depression.

And dopamine production is regulated by tyrosinase activity. Tyrosinase can directly oxidise dopamine into toxic aminochromes. An aminochrome:

forms adducts with proteins such as alpha-synuclein-inducing and alpha-synuclein-stabilizing neurotoxic protofibrils.

The aggregation and misfolding of these alpha-synuclein protein adducts into Lewy bodies is thought to accelerate the death of the neuronal cells in the brain, which then precipitates Parkinson’s disease. Some of these aminochromes can also end up tautomerising and polymerising into neuromelanin.

Of course, in some situations, dopamine can become oxidised by the oxidative stress that is caused by the reactive oxygen species that spill out of our cellular mitochondria during the energy generation process.