Posted by Larry Hoover on April 9, 2003, at 11:59:50
In reply to Re: clarification, posted by Larry Hoover on April 9, 2003, at 9:12:48
>Later, when it was found that there were a number of different 18-carbon fatty acids with two double bonds (what chemists call positional isomers), to tell *them* apart, one was designated alpha, another beta, and the third gamma (ALA, BLA, and GLA). Today, we know flax as a good source of alpha-linolenic acid (ALNA, note the extra "n"), an omega-3 fatty acid with three double bonds.
Geez, I've seen this wrong so many times all over the web that I made the same error.
The alpha- beta- gamma- bit refers to isomers of linolenic (note the "n"), not linoleic acid. Linolenic acid has three positional isomers. The alpha version is omega-3. The gamma version is omega-6. I have no idea what the beta version is, for sure.
I think in an entirely different nomenclature (called IUPAC nomenclature, which stands for International Union of Pure and Applied Chemistry). The whole point of IUPAC nomenclature is to avoid errors of this type. Names like linoleic and linolenic are called trivial names, and they can be very confusing.
In IUPAC terminology, alpha-linolenic acid is (delta)9,12,15-octadecatrienoic acid. Gamma-linolenic is (delta)6,9,12-octadecatrienoic acid. In these explicit terms, once you know that octadeca means 18, and trien(e) means triply unsaturated, and the numbers are counted from the acid end, you can derive the omega positions for the double bonds. They are 18 minus 15 (omega-3), and so on.
I'm having computer problems (mouse weirdness). It didn't work right for hours, but I got it working again. If I disappear, blame technology.
Lar
poster:Larry Hoover
thread:217108
URL: http://www.dr-bob.org/babble/20030407/msgs/217807.html