Ben Benevenga
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Ben Benevenga |
The outline below lists the speakers for the symposium.
CD copies of the entire symposium
can be obtained from Tom Crenshaw (crenshaw@calshp.cals.wisc.edu) These presentations
offer unique perspectives for professional nutritionists and scientists with
interest in amino acid metabolism. Great supplemental materials for graduate
level nutrition courses.
Read the transcripts below of a stimulating discussion that followed a 4.5 hr symposium on amino acid metabolism by the world's expert's on amino acid nutrition.
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Ben Benevenga |
Vernon Young |
Vernon Young. In terms of the recovery of nitrogen, I really thought Ben was on to a big win a number of years ago when he told me the design of his infusion experiments, and so on and so forth. And I suppose, Ben, you didn't pursue the N-15, uh, tool? That might have helped you determine whether or not N-15 actually appeared as a volatile, as a gaseous end product of the nitrogen that you were infusing as alanine. Is that correct? I know you did very careful balance measurements. You looked at urine, you looked at the carcass and so on. But did you look at the gaseous environment?
Ben Benevenga. That was the one poster that you missed, Vernon.
(laughter)
Vernon Young. I missed a lot of posters.
Ben Benevenga. We did do that. And Tom Rasch and I chased that nitrogen with 15 N-alanine infused over about 60 hours. And we collected expired air. We actually did keep a pig in an argon-oxygen environment for about 70 hours. And over every six hours, we took gas samples out of the chamber and did mass-spec analysis and we looked for N-29 and N-30. We didn't see any. In fact, we saw no evidence of a gaseous volatile compound. And I haven't chased that any further than that. The one place I haven't looked would be on the soda-sorb that we had in-line. And I have that. But in retirement, I may get a chance to look for that.
Vernon Young. I'd like to come back Dave, in a sense, to your challenge about sulfur amino acid relationships, and so on. And as you know, at least in terms of the way we've approached this, we have not been able to confirm a physiological, if you like, sparing of the methionine requirement. Which it's sort of very well established in the animal nutritional context, and very definitely well established in more biochemical, in vitro, enzyme, and Jim Finkelstein contexts, and so on. And as you know, we concluded that, from a nutritional point of view, we've been able to, unable to, confirm a cysteine-sparing of methionine. Although, we're careful to point out that this doesn't refute the fact, that you can show it biochemically, providing the levels of cysteine are sufficiently high, as far as I can judge, to inhibit the activity of cysteine beta-synthase and so on.
And I think when we get methionine within, and cysteine within certain nutritional ranges, we don't change, for example, plasma cysteine levels to a point at which it might actually have an inhibitory effect on the trans-sulfuration pathway.
And furthermore, as you well know,
there's very significant first-pass disappearance, and possibly even in the
intestine, based on Martha’s (Stipanuk) work, with cysteine, which doesn't
actually get to the liver and the tissues where methionine catabolism is occurring.
So, I think that is the source of explanation as to why we do not see what we
think is a methionine-sparing by cysteine. The evidence is kinetics, the lack
of change of oxidation of methionine.....
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