Methionine content of dietary proteins affects the molecular species composition of plasma phosphatidylcholine in rats fed a cholesterol-free diet.
The effects of dietary protein types and methionine supplementation on phospholipid metabolism were investigated to clarify the mechanism of the hypocholesterolemic action of soybean protein in rats fed a cholesterol-free diet. The effect of switching from a casein diet to a soybean protein diet was also investigated. Rats were fed casein, soybean protein or soybean protein + methionine diet for 14 d. Compared with casein diet, feeding of soybean protein diet led to significantly higher proportions of linoleic acid and linoleic acid-containing molecular species, especially 16:0-18:2, in plasma and liver microsomal phosphatidylcholine (PC). In addition, significantly lower plasma cholesterol concentration, hepatic S-adenosylmethionine concentration and liver microsomal PC:phosphatidylethanolamine ratio resulted. These alterations caused by the soybean protein diet were significantly suppressed by supplementing methionine to the level of the casein diet (3.4 g/kg diet). The proportion of the sum of certain plasma PC molecular species, which contain 18:1 or 18:2 in the sn-2 position, increased in response to the switch from the casein diet to the soybean protein diet at a rate similar to the decrease in plasma cholesterol concentration; there was a significant correlation between the two variables (r = -0.992, P < 0.001). These results indicate that about 40% of the hypocholesterolemic action of soybean protein is due to the low methionine content of the protein and might be associated with alterations of the plasma phospholipid molecular species profile.
Sugiyama
K
K
Department of Applied Biological Chemistry, Faculty of Agriculture, Shizuoka University, Japan.
Yamakawa
A
A
Kumazawa
A
A
Saeki
S
S
D000818:Animals; D002784:Cholesterol / Q000097:blood*; D002791:Cholesterol, Dietary / Q000008:administration & dosage*; D004044:Dietary Proteins / Q000494:pharmacology*; D005227:Fatty Acids / Q000032:analysis; D008297:Male; D008715:Methionine / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D010713:Phosphatidylcholines / Q000097:blood* / Q000737:chemistry; D051381:Rats; D017208:Rats, Wistar; D013025:Glycine max
D002791:Cholesterol, Dietary; D004044:Dietary Proteins; D005227:Fatty Acids; D010713:Phosphatidylcholines; D002784:Cholesterol; D008715:Methionine