Genetic engineering eases laundry woes.

Help is on the way for those who occasionally forget the Golden Rule of Laundry: Carefully separate the whites from the colors, lest your underwear emerge tinted pink from a stray red sock

Researchers at Novo Nordisk Biotech in Davis, Calif., and its parent company in Bagsvaerd, Denmark, report a new detergent additive that can help prevent these laundry accidents. They began with a mushroom enzyme, called heme peroxidase, that can oxidize dyes and thus remove their colors. Then they genetically engineered it to survive in hot, soapy water, even with bleach.

Guided by the enzyme's three-dimensional structure, the Novo Nordisk scientists first changed four amino acids to improve its stability. They also used a technique called directed evolution (SN: 5/9/98, p. 296) to make it more robust.

They searched for other key amino acid locations by randomly mutating the enzyme, creating tens of thousands of variations. They selected the ones that functioned best and repeated the process, eventually yielding a set of about 100 enzymes.

Although improved overall, each of these enzymes could harbor both good and bad mutations, says Novo Nordisk's Joel R. Cherry. To weed out detrimental changes, he and his colleagues cut the enzymes into fragments, each containing one mutation. Using the biochemical machinery of yeast, they randomly recombined the pieces in a process known as DNA shuffling.

Again, they screened tens of thousands of variations to find the best mix of mutations. The final enzyme, having seven amino acid changes, is 174 times more heat resistant and 100 times more chemically stable than the natural version. The group reports its results in the April NATURE BIOTECHNOLOGY.

"It's a nice example of how directed evolution can solve a difficult problem," says Frances H. Arnold of the California Institute of Technology in Pasadena. However, she suspects that in general, this wouldn't be an efficient strategy to engineer enzymes because such a large number of variants must be screened.

The potential laundry additive, like polymers already on the market, only picks up dye from the wash water, not from underwear already turned pink.