Cancer, deep-sea partnerships and the resented carbon-tax

 “We shouldn’t be looking for heroes, we should be looking for good ideas.”

-Noam Chomsky

Forgive me this indulgence, but rather than devote the usual 500 to 1200 words to a given topic, I would like to scan a trio of topics and ideas that have caught my attention in the past week.

  1. The mantra “everything causes cancer” is far-removed from the truth. Out of the literally millions of known mixtures, compounds and elements, less than 500 are proven or probable carcinogens. As children and young adults, many of us never suspected city air, processed meat and alcohol to be among the culprits. This unfortunately leads some of us to wave the white flag and adopt the erroneous generalisation. But that defeatist attitude is music to the ears of the carcinogens’ users and producers who refuse to acknowledge responsibility. Speaking of music,  sound is a form of energy, and along with radio waves and all the colours of the rainbow—none of those, unlike ultraviolet, x-rays and gamma, cause cancer.
  2. Something a little newer and more original. If as a teacher or student you hear of an oxidation-reduction partnership, the words might conjure up an image of people partnering up to do a redox lab. But until recently, not even the most specialized biochemists imagined that two different organisms were symbiotically working together to oxidize methane and reduce sulfate, respectively, in layers of sediment and rock under the sea floor. MethanogenOne of the microbes, a methanotroph which uses methane (CH4) as its energy and carbon source, reduces CH4 to hydrogen carbonate ion (HCO3) in the absence of oxygen. But the metal ions that the organism uses to pick up electrons lost by methane are not efficient enough. A sulfate-reducing bacteria comes to the rescue. It uses the electrons released by the oxidation of methane to reduce sulfate (SO42-) to sulfide (S2-). Its reward? It too obtains energy in the process.
  3. There have been riots in Paris in early December 2018 over the proposed fuel tax. Since France does not generate very much CO2 in generating electricity (70% of the country’s power comes from nuclear energy), it would make more sense for them to subsidise electric car purchases and taxing new gasoline- powered automobiles. I’m never one to defend internal combustion automobiles, but let’s bear in mind that the entire transportation sector including ships, trains, planes and automobiles account for only 14% of carbon emissions. 20152C_GHGSectors_GlobalAnd then what impact will higher fuel prices actually have on consumption and consequent emissions? Even if it doesn’t lower emissions immediately, there’s another layer of strategy behind a carbon tax. It creates a pool of funds which can can then be used as incentives to lower emissions. For example, the money can be used to set up charging stations for electric cars. In Quebec the carbon tax has created a fund of close to a billion dollars but as of December 2018, it has not been managed properly. The new CAQ government in this province is not looking to abolish the tax but is looking into ways of assuring to meet the 2020 goal of cutting emissions by 20% compared to 1990 levels.
    paris-riots-emmanuel-macron-yellow-jackets
    More carbon emissions from the violent protesters in Paris. From Newsweek, Dec 2 , 2018

    Governments, however, need to quickly use a comprehensive approach so that all emissions are addressed and abated. The current narrow-minded focus on taxation of fuel won’t cut it. This is exacerbated by the fact that environmental values are are not deeply held and shared by enough people. As a result every mantra: “eat less meat”, “drive less”, “preserve forests”, etcetera, gets misinterpreted as an authoritative order. And too many of us are so talented at cutting our noses to spite the face of government. As an alternative strategy, the federal government can nourish the roots of the environmental grass movement. I know schools are asked to do an awful lot these days. But most schools do next to nothing about climate change. Yet they seem to find the time to peddle an awful lot of electronics and student travel. Here’s a list of things schools can do to be proactive about climate change.(1) Encourage teachers to use public transit or electric cars and not fill the parking lot with 19th century inventions.

    (2) Compost cafeteria waste.

    (3) Reduce and reuse before dumping stuff into recycling bins.

    (4) Reward students for coming up with green ideas.

    (5) Serve beef sparingly in the cafeteria. Replace it with more chicken meals, which have a much lower carbon footprint.

    (6) Encourage local travel instead of flying or driving to remote destinations.

Sources:
Nature Communications. Carbonate-hosted methanotrophy represents an unrecognized methane sink in the deep sea
www.nature.com/articles/ncomms6094
Scientific American The Mystery of the Missing Molecules scientificamerican/journal/v319/n5/box/scientificamerican1118-32_BX1.html
(has more subsequent reactions)

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Hot Chili Pepper Chemistry

The English word pepper is ambiguous. Botanically it could be refer to plants that produce black powdered pepper. The angiosperms (flowering plants) who serve as a source of that spice belong to the order Piperales and to the 3600-member family Piperaceae. (Kings play chess only for goodness’ sake is a mnemonic for remembering the order of biological classification: kingdom, a group of related phyla, which in turn, at least in singular form, phylum, is a group of related classes, and so on with orders, families, genera and species. ) Piperine is the compound mainly responsible for black pepper’s pungency, but as expected it does not appear in unrelated plants also dubbed as peppers.

1280px-Ripe_jalapeno_pepper
In jalapeños,  dihydrocapsaicin and capsaicin, are the two  amides mainly responsible for their hotness.

Pepper can also refer to Capsicum chinense, the Red Savino haanero chili, a member of the tomato family, Solanacea.  That fruit scores in the hundreds of thousands of units on the Scoville scale of “hotness”.  Other hot  peppers and milder ones are found among the many varieties of another Capsicum species, known as annum, which includes sweet peppers, jalapeños, and New Mexico chili.

 

There are four different amides (specifically, capsaicioids) found in hot peppers of the Capsicum genus. A Brazilian study revealed that in these fruits capsaicin makes up anywhere from 24% (in jalapeños) to 95% (pimenta preta) of capsaicioids present. These in turn combine to account anywhere from 0.2 mg to 7 mg per gram of fresh pepper, in other words, less than 1%. The percentage of course soars when the pepper is dried. Except in jalapeños and fatalis, the equally potent compound, dihydrocapsaicin, is the second most abundant amide. The greatest concentration (9.2%) of nordihydrocapsaicin, a substance about half as hot, was found in pimenta de mesa. Finally another related compound, homocapsaicin, the least potent of the quartet, is entirely absent from most spicy peppers, but it makes up 12% of dedo-de-moça pequena’s capsaicioids.

Nordihydrocapsaicin
nnordihydrocapsaicin 9 100 000
Dihydrocapsaicin
dihydrocapsaicin 16 000 000
Homocapsaicin
homocapsaicin 8 600 000
capsaicin
capsaicin 16 000 000
pimenta de mesa
The hot amides in pimenta de mesa consist of about 53% capsaicin, 37% dihydrocapsaicin, 1% homocapsaicin and about 9% nordihydrocapsaicin . The latter’s concentration is not surpassed in 20 other species of Capsicum.

From examining the above structural diagrams notice that in comparison to capsaicin,  homocapsaicin’s double bond is slightly further away from the tail end of the molecule. On the other hand, nordihydrocapsaicin’s strength is compromised by being one CH2 shorter than its hotter counterpart, dihydrocapsaicin.

How do these compounds exert such a powerful reaction in our mouths? In all mammals they cause tingling and burning sensations by activating  a non-selective cation channel, called VR1, on nerve endings. It’s not a coincidence that the same channel also interacts with compounds released by inflammation from actual intense heat sources or acidic protons. Birds, however, have a variant of VR1, which is still sensitive to heat and acid but which does not interact with capsaicin or its analogues.  It’s likely an example of co-evolution between Capsicum plants and animals who can eat their fruits without suffering deterring consequences. They then fly to other destinations to spread ingested seed.
We get more evidence of coevolution thanks to Jordi Altimiras of  Linköping University who made me aware of a study revealing that chilli seed germination is decreased in the gastrointestinal tract of mammals but not by the passage through the tract of birds.

Finally why are peppers producing capsaicioids in the first place? Any biosynthesis is catabolic and thus consumes energy. But making capsaicinoids in fruits is a worthwhile investment; it reduces fungal infection and seed mortality. From that narrow perspective we mammals have more in common with fungi than birds.

Sources:

  • Molecular basis for species-specific sensitivity to “hot” chili peppers.  2002 Feb 8;108(3):421-30.
  • Comparative Study of Capsaicinoid Composition in Capsicum Peppers Grown in Brazil
    http://www.tandfonline.com/doi/full/10.1080/10942912.2015.1072210
  • Directed deterrence by capsaicin in chillies. Nature 412: 403-404 and Tewksbury JJ, Reagan KM, Machnicki NJ, Carlo TA, Haak DC, et al. (2008)
  • Evolutionary ecology of pungency in wild chilies. ProcNatAcadSciUSA 105: 11808-11811 .

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