Methionine Metabolism in Piglets Fed dl-Methionine or Its Hydroxy Analogue Was Affected by Distribution of Enzymes Oxidizing These Sources to Keto-Methionine

Abstract

Previous evidence shows that the extensive catabolism of dietary essential amino acids (AA) by the intestine results in decreased availability of these AA for protein synthesis in extraintestinal tissues. This raises the possibility that extraintestinal availability of AA may be improved by supplying the animal with an AA source more of which can bypass the intestine. To test this hypothesis, six barrows (35-day-old, 8.6 +/- 1.4 kg), implanted with arterial, portal, and mesenteric catheters, were fed a DL-methionine (DL-MET) or DL-2-hydroxy-4-methylthiobutyrate (DL-HMTB) diet once hourly and infused intramesenterically with 1% p-amino hippurate. Although the directly available L-MET in DL-MET diet was about 1.2-fold that in DL-HMTB diet, the net portal appearance of L-MET was not different between the two diets. Compared with the low mRNA abundance and low activity of D-2-hydroxy acid dehydrogenase (D-HADH) and l-2-hydroxy acid oxidase (L-HAOX) in the intestine, the high mRNA abundance and high activity of D-AA oxidase (D-AAOX) indicated that the intestine had a relatively higher capacity of D-MET utilization than of dl-HMTB utilization to L-MET synthesis and its subsequent metabolism. However, in contrast to the much lower D-AAOX activity (nmol/g tissue) in the stomach than in the liver and kidney, both d-HADH and L-HAOX activity in the stomach was comparable with those in the liver and/or kidney, indicating the substantial capacity of the stomach to convert DL-HMTB to L-MET. Collectively, the difference in distribution of activity and mRNA abundance of D-AAOX, D-HADH, and L-HAOX in the piglets may offer a biological basis for the similar portal appearance of L-MET between DL-MET and DL-HMTB diets, and thus may provide new important insights into nutritional efficiency of different L-MET sources.

Effects of dietary methionine supplementation on growth performance, intestinal morphology, antioxidant capacity and immune function in intra‐uterine growth‐retarded suckling piglets

“…All D -Met can be converted to L -Met by pigs (Kong, Park, Ahn, & Kim, 2016;Wretlind & Rose, 1950), because the capacity of the ratelimiting enzyme D -amino acid oxidase ( D -AAOX) to convert D -Met to L -Met is present in different tissues including liver, kidney, stomach, duodenum, jejunum and ileum (Fang et al, 2010). Indeed, several studies have reported that the pigs fed diets supplemented with L -Met had no differences in growth performance when compared with the pigs fed with DL -Met-supplemented diets (Chen, Piao, Zhao, & Zeng, 2013;Chung & Baker, 1992;Htoo & Morales, 2016;Kong et al, 2016;Tian, Zeng, Zhang, Long, & Piao, 2016 (Han et al, 2013;Wang et al, 2005;Xu, Mellor, Birtles, Reynolds, & Simpson, 1994).…”

Effects of dietary supplemental methionine source and betaine replacement on the growth performance and activity of mitochondrial respiratory chain enzymes in normal and heat‐stressed broiler chickens

“…Our data provided evidence to support earlier results indicating that the effectiveness of dl ‐Met is similar to that of l ‐Met in chicks (Chung & Baker, ; Dilger & Baker, ). Fang et al () stated that the conversion of d ‐Met to l ‐Met is not a limiting factor due to the existence of substantial d ‐amino acid oxidase activity in all along the GIT, the kidney and the muscles and the genes responsible are activated in the presence of this molecule. However, there are some reports showing that l ‐Met is better utilized by broiler chicks compared to d ‐Met (Shen et al, ; Shen, Weaver, & Kim, ).…”

Bioavailability ofl-methionine relative todl-methionine in Broiler chickens

“…DL-Met (an equal racemic mixture of the D-and L-isomers of Met) is commonly added to poultry feeds that are low in natural Met to satisfy the requirement of chickens for this amino acid. However, only L-isomer that had been commercially available by a fermentation approach recently (Huang et al 2017), is the biologically functional form of Met, as it can be used readily in intestinal cells and directly incorporated into protein synthesis (Fang et al 2010). It is indispensable that dietary D-Met is converted to L-Met in a process catalysed by D-Met oxidase that resides in liver, kidney and intestines prior to its utilisation (Fang et al 2010).…”

“…However, only L-isomer that had been commercially available by a fermentation approach recently (Huang et al 2017), is the biologically functional form of Met, as it can be used readily in intestinal cells and directly incorporated into protein synthesis (Fang et al 2010). It is indispensable that dietary D-Met is converted to L-Met in a process catalysed by D-Met oxidase that resides in liver, kidney and intestines prior to its utilisation (Fang et al 2010). However, the oxidative activity towards D-Met exists in the intestine only represents about one-half and onetenth of the hepatic and renal activity, respectively (Brachet and Puigserver 1992).…”