14 June 2014 | NewScientist | 19

No need to shiver to lose excess flab

BEING cold can burn calories, but no

one wants to freeze just to ditch

their muffin top. Soon we may not

have to. It seems that immune

molecules normally triggered by

cold temperatures can make fat

mice lose weight — without the

need for the mercury to drop.

Humans respond to cold in two

ways: we shiver to produce a quick

burst of heat, and as Ajay Chawla at

the University of California, San

Francisco, recently discovered,

immune signals get sent to

molecules called macrophages.

These release other molecules that

convert white fat, the sort that

stores energy, into another type

that burns energy: brown fat.

Now Chawla’s team have found

the signalling molecules that

kick-start this transition. By giving

obese mice a dose of one of these

molecules, interleukin-4, four times

over eight days, the team was able

to activate the immune system’s

response to cold.

Two weeks, later the mice had lost

12 per cent of their weight, they had

4 grams of brown fat where there

was none before, and they were

metabolising 10 per cent more

energy (Cell, doi.org/s4r). The effect

might be less dramatic in humans as

we are less efficient at making

brown fat. “But increasing energy

expenditure by a few per cent can still

have a huge effect,” says Chawla.

Forehead and fingertips pick up pain

OUCH! Forehead and fingertips are

the body parts most sensitive to pain.

Our ability to work out where

something hurts – “spatial acuity” –

varies across the body. To work out

which areas are most sensitive,

Flavia Mancini at University College

London and her colleagues delivered

sharp shocks to 26 volunteers using

two small lasers. The distance

between the lasers was reduced until

they were indistinguishable. This

was then repeated all over the body.

The volunteers could distinguish

between the two lasers more

accurately at areas closest to their

trunk, and less so towards the

extremities – the opposite of how

we feel touch. But there were two

exceptions: they did best on the test

on their fingertips and forehead

(Annals of Neurology, doi.org/s4t).

This is surprising because there

are few pain-triggering nerve fibres

in these areas, says Mancini. So we

must have learned to localise pain

there despite a sparsity of fibres.

A test that distinguishes pain from

touch is important because people

who have long-term chronic pain

need to identify which set of fibres

are involved, Mancini says.

A CHEMICAL chimera may one day help make better biofuel. The feat involves mixing enzymes from two types of plant-munching bacteria that would never have met in nature.

Biofuel is made from the sugars in crops such as corn. This alternative fuel is more climate friendly than gas or coal. But even better would be biofuels that use cheap, widespread plant matter such as leaves and grasses rather than food crops. The trouble is, those parts of plants are high in cellulose, a sturdy

structural compound that is hard to break down.

Microbes living in oxygen-rich environments use enzymes floating free inside their cells to digest such plant matter. Bacteria that live in places with low or no oxygen instead use complex scaffolds of enzymes known as cellulosomes. Free enzymes are fast-acting, while cellulosomes are slower but highly efficient.

Yonathan Arfi and Ed Bayer at the Weizmann Institute of Science in Rehovot, Israel, designed a chemical reaction that fused a

free-floating enzyme particularly effective at breaking down cellulose onto a cellulosome. The resulting hybrid is both quick and efficient at turning cellulose into useful sugars (PNAS, DOI: 10.1073/pnas.1404148111).

Bayer says the advance is not yet enough to make better biofuels, but it boosts our understanding of the agents involved. Vincent Eijsink at the Norwegian University of Life Sciences in Ås says research like this could make possible a new generation of efficient biofuels that don’t rely on food crops.

Hybrid enzymes may be a biofuel boon

Tune in, swim down, suck worms

IT’S not quite what Timothy Leary had in mind when he advocated the use of acid. The Japanese sea catfish is the first fish known to hunt its prey using changes in water acidity.

The catfish (Plotosus japonicus) feeds on worms living in tunnels dug into the seabed. John Caprio of Louisiana State University in Baton Rouge and his colleagues already knew that the fish rapidly home in on the worms’ tunnels but ignore unoccupied ones.

Caprio assumed that the catfish could smell chemicals from the worms. So his team applied these one after another to the fish’s whiskers to find out which ones triggered the hunting behaviour.

Instead, they found the fish responded most to slight variations in the acidity of seawater. The worms breathe out carbon dioxide, which reacts with water to form carbonic acid, slightly acidifying it. That increase in acidity was enough to get the fish hunting (Science, doi.org/s4p).

But the fish missed changes in acidity if the water was too acidic. The oceans are becoming more acidic due to global warming, and this acidification might mean they soon struggle to find prey.

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