Quantitative study in vivo of methionine cycle in humans using (methyl-/sup 2/H/sub 3/)- and (1-/sup 13/C)methionine

Journal Article · Thu Sep 01 00:00:00 EDT 1988 · Am. J. Physiol.; (United States)

OSTI ID:6746170

Storch, K J; Wagner, D A; Burke, J F; Young, V R

Kinetic aspects of body methionine (MET) metabolism were examined in healthy young men during the fed and postabsorptive (PA) states. Rates of MET incorporation (S) into and release (B) from body proteins; transmethylation (TM); and remethylation (RM) and transsulfuration (TS) of homocysteine (HCY) were estimated with the aid of a 5-h constant intravenous infusion of (methyl-2H3)- and (1-13C)methionine. The isotopic data (plasma methionine labeling and 13C enrichment of expired air) were submitted to a stochastic model of amino acid metabolism. During the fed state, the subjects (n = 4) received, at 20-min intervals, small isonitrogenous isocaloric meals containing a complete L-amino acid mixture supplying MET at a rate equivalent to 198 mumol.kg body wt-1.day-1. The PA subjects (n = 4) received the isotope after a 10-h overnight fast. For the PA group, the components of MET metabolism were as follows: S, 20 +/- 0.5; B, 24 +/- 0.5; TM, 5.8 +/- 0.6; RM, 1.8 +/- 0.4; and TS, 4.0 +/- 0.4 (+/-SE) mumol.kg-1.h-1. During the fed state the values were S, 26 +/- 2.5; B, 18 +/- 2; TM, 14 +/- 1.3; RM, 5.7 +/- 0.9; and TS 8.3 +/- 0.6 mumol.kg-1.h-1. The meal-induced changes in B, TM, RM, and TS were significant (P less than 0.05). Comparison of the partitioning of MET between S and TM (these two pathways of MET disposal constitute the ''methionine locus'') in the PA and in the fed states indicates that the MET locus is of regulatory importance in MET homeostasis. A twofold increase in the partitioning of MET to TM was observed in the fed state. The increase in HCY recycling, relative to TS (these two pathways of HCY disposal constitute the ''HCY locus''), in the fed state did not reach statistical significance when compared with the PA state. Total daily TM are estimated to be 238 +/- 22 mumol/kg. This is similar to the estimate generated by the methyl balance model of Mudd and Poole which approximated 241 mumol/kg.

• Research Organization: Massachusetts Institute of Technology, Cambridge (USA)
• OSTI ID: 6746170
• Journal Information: Am. J. Physiol.; (United States), Vol. 255
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
METHIONINE
METABOLISM
BIOLOGICAL PATHWAYS
CARBON 13
DEUTERIUM
DIET
FASTING
HOMEOSTASIS
MATHEMATICAL MODELS
TRACER TECHNIQUES
AMINO ACIDS
CARBON ISOTOPES
CARBOXYLIC ACIDS
DRUGS
EVEN-ODD NUCLEI
HYDROGEN ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
LIPOTROPIC FACTORS
NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
STABLE ISOTOPES
550501* - Metabolism- Tracer Techniques