ONE of biology鈥檚 fundamental building blocks has a flair for catalysing
chemical reactions. Leucine, one of the 20 amino acids from which nature
constructs proteins, could serve as a cheap and environmentally friendly
catalyst for industry when polymerised into short chains of between 15 and 30
leucine units to make polyleucine.
Stan Roberts and his colleagues at the University of Liverpool followed up
early hints, published in the 1980s, of polyleucine鈥檚 catalytic power. They have
now proved that the amino acid excels at catalysing a chemical reaction called
epoxidation, which inserts an oxygen atom into organic molecules at points where
carbon atoms are connected by double bonds. The added oxygen atom forms a
triangle with the two carbons.
The researchers, who will report their results in Chemical
Communications at the end of this month, have catalysed around 100
reactions with polyleucine. Already, they have shown that it could provide a
cheaper method for making diltiazem, a drug for treating angina.
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More importantly, they found that some epoxide molecules can be made in a
鈥渓eft-handed鈥� shape or its 鈥渞ight-handed鈥� mirror image, simply by switching from
left-handed polyleucine to the right-handed form. This distinction can be
important for drugs, as the two forms can have different effects in the
body.
Because polyleucine forms an insoluble goo, it can be filtered off afterwards
and reused. 鈥淚t鈥檚 so childishly simple,鈥� says Roberts. More intriguingly, he
speculates that polyleucine might have been one of nature鈥檚 first catalysts, and
may have helped to create the first sugars.
Roberts has shown that other polymerised amino acids, including polyalanine
and polyvaline, serve as catalysts too. 鈥淭his is only the start,鈥� he says.