karl@spruce.gsfc.nasa.gov (karl anderson) (05/16/91)
In article <1991May16.030620.24749@menudo.uh.edu>, davison@menudo.uh.edu (Dan Davison) writes: |> In article <1991May14.102820@quercus.gsfc.nasa.gov> |> karl@quercus.gsfc.nasa.gov (Karl Anderson) writes: |> |> Human metabolism can synthesize all but seven (the "essential" |> amino acids) of the twenty; they must get those seven from |> their food. |> [..] |> |> Nope, it's nine. The essential: histidine, isoleucine, leucine, |> lysine, methionine, phenylalanine, threonine, tryptophan, valine. |> |> The non-essential: alanine, arginine, asparagine, aspartate, |> cystenine, glutamate, glutamine, glycine, proline, serice, and |> tyrosine. |> |> How did you get 7? I don't see any interconversion pathways in |> humans listed...perhaps you were counting salvage pathways? |> |> source: Stryer, "Biochemistry", 3d. ed, pg. 578. |> |> I just finished teaching this a few weeks ago! |> Um, I should have checked my copy of Stryer (1st ed). On page 503 he says "Humans can synthesize only half the basic set of twenty amino acids (Table 21-1). These amino acids are called nonessential, whereas the ones that must be supplied in the diet are called essential. These terms refer to the needs of an organism under a particular set of conditions. For example, enough arginine is synthesized by the urea cycle to meet the needs of an adult but not those of a growing child. A deficiency of even one amino acid results in a *negative nitrogen balance* [Stryer's emphasis]. In this state, more protein is degraded than is synthesized, and so more nitrogen is excreted than is ingested." Table 21-1 lists arginine along with the ones you give as essential. Is this the current understanding, Dan? The figure 7 was dredged up from imperfect memory - I took biochem 12 years ago. Thanks for giving us an authoritative answer to the original question. I think this group needs more of this kind of rigor. -- Karl A. Anderson | Internet: karl@forest.gsfc.nasa.gov NASA/GSFC code 923 (STX) | voice: (301) 286-3815 Greenbelt, MD 20771 | #include "std_disclaimer"
davison@menudo.uh.edu (Dan Davison) (05/18/91)
|> Nope, it's nine. The essential: histidine, isoleucine, leucine, |> lysine, methionine, phenylalanine, threonine, tryptophan, valine. |> The non-essential: alanine, arginine, asparagine, aspartate, |> cystenine, glutamate, glutamine, glycine, proline, serice, and |> tyrosine. Table 21-1 lists arginine along with the ones you give as essential. Is this the current understanding, Dan? Hmmm. Mathews and Van Volde list 10, the nine above plus arginine. (p. 681). Leningher lists those 10. White, Handler and Smith list those 10. Voet and Voet list those 10. The difference appears to be rate-dependent and opinion-dependent . The most mammals *do* synthesize arginine, so it is not essential in that the aa cannot be synthesized. But rats do not synthesize enough and all mammals break arginine down to urea as part of the urea cycle, so there just isn't enough around for normal growth. So, there are two classes of "essential" as used in the textbooks: 1) able to be synthesized de novo and 2) able to get enough for normal growth demands. dan -- dr. dan davison/dept. of biochemical and biophysical sciences/univ. of Houston/4800 Calhoun/Houston,TX 77054-5500/davison@uh.edu/DAVISON@UHOU Disclaimer: As always, I speak only for myself, and, usually, only to myself.