Homoserine dehydratase activity is a measure of cystathionase, an enzyme which catalyses the last step leading to cysteine formation in the transsulphuration pathway. The enzyme develops rapidly in fetal rat liver starting on the 20th day of gestation and reaches its adult level on the 2nd day after birth. It cannot be prematurely induced by treatment of fetal animals with glucagon, hydrocortisone or thyroxine, which are effective in elevating other enzymes in the same experiments. Glucagon treatment significantly raised the enzyme level in 30-day-old rats. With the prenatal development of this enzyme,all three enzymes for the conversion of methionine to cysteine are functional in rat liver at the time of birth, so that cysteine cannot be an essential amino acid in the infant rat as has been suggested for the human infant.

Keywords:
Transsulphuration, Neonatal development, Hormonal effects, Rat liver, L-Homoserine dehydratase, Cystathionase, Cysteine
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1972
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