prior exposure of rats to a mixture of nitrous oxide/oxygen ( 80/20 ) for 20 to 24 hours and feeding rats a diet deficient in vitamin b-12 and methionine for 23 weeks resulted in a 86 to 90 % decrease in the activity of the vitamin b-12 dependent enzyme , 5-methyltetrahydrofolate-homocysteine methyltransferase ( ec 4.2.99.10 ) .
C0042847
deficient
C0042845
vitamin b-12