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What scientists really want to know is what membrane components are near what other components, how that organization changes over time and how that organization leads to the emergence of function, Boxer said.

In their experiment, the scientists analyzed a model system to reveal its lateral organization. First they used lipids with either ''short'' or ''tall'' chemical structures to create phase domains, or membrane features that they could study. Tall lipids, red in illustrations in the paper, melted at higher temperatures than short lipids, represented by green. The researchers melted the lipids together, then placed them on a surface to cool and separate into splotchy patterns. This is the system that Longo had developed for other purposes in earlier work.

''The tall guys tend to like each other and the short guys tend to like each other and shorts and talls tend to separate,'' Boxer said. ''Like likes like.''

Kraft had labeled the short and tall lipids with isotopes-elements that compare exactly in chemical properties because they have the same number of protons but that differ in mass because they have a different number of neutrons. Isotopes do not change the chemical structure of the molecules that they label. In contrast, the dyes commonly used in biological studies for labeling change the structure of the molecules to which they attach and can alter their behavior. Moreover, dyes do not allow scientists to analyze membrane compositions, because scientists see only what they've labeled.

''If you want to look at lipids certainly, lipid organization, you need some other way [than dyes],'' Boxer said. ''You'd want to have a way that's specific, that tells you which component is which. I'll put on my chemist hat now. When a chemist says, 'I know what's there,' he or she means, 'I know chemically what's there.'
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Source:Stanford University