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Updated: Jul 12, 2026

Metabolic Pathway Confirmation and Discovery Through 13C-labeling of Proteinogenic Amino Acids
Published on: January 26, 2012
2-Hydroxy-4-(methylthio) butanoic acid is a naturally occurring methionine precursor in the chick
J J Dibner1, R C Durley, J G Kostelc
1Monsanto Company, Animals Sciences Division, Chesterfield, MO 63198.
Abstract:
The objective of these experiments was to determine the origin of 2-hydroxy-4-(methylthio)-butanoic acid (HMB) detected in the liver and excreta of chicks that had never been fed Alimet (an 88% aqueous solution of HMB) or MHA (an 86% calcium salt of HMB). Gas chromatography and mass spectrometry were used to identify HMB in these birds. A normal biochemical pathway of 5'-deoxy-5'-methylthioadenosine (MTA) is proposed as the source of naturally occurring HMB. Studies of conversion of [methyl-14C]MTA to L-methionine by chick liver enzymesØe showed that radiolabeled HMB and 2-oxo-4-(methylthio)butanoic acid (keto-methionine) were synthesized during the reaction. Specific radioactivities of labeled HMB and keto-methionine showed that HMB is not synthesized from keto-methionine. Fractionation studies indicated that radiolabeled HMB formed from [14C]MTA could be used in the synthesis of L-methionine in the presence of peroxisomes and/or mitochondrial enzymes. In this way, HMB synthesized from MTA by chick liver enzymes functions as a precursor of L-methionine and as an intermediate in a naturally occurring pathway for the synthesis of L-methionine in the chick.
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