y-glutamyl transpeptidase and amino acid transport for
milk protein production in vivo
JOHNSTON, S.L., ROY, N.C., DAVIS, S.R., TWEEDIE, J.W., KITSON,
K.E. AND LEE, J.
AgResearch Limited, Grasslands Research Centre, Private Bag 11
008, Palmerston North
E-Mail:
Proceedings of the New Zealand Society of Animal Production 2001. 61:
244-247
Activity of the enzyme y-glutamyl transpeptidase
(y-GT) (EC 2.3.2.2) a putative facilitator of amino acid (AA)
transport in the mammary gland, increases before lactation and decreases
at weaning, suggesting a role in AA transport for milk protein
synthesis. The effect of y-GT inhibition by acivicin and supply
of cyst(e)ine from N-acetylcysteine (NAC) on mammary AA uptake and milk
production was studied in lactating goats. NAC increased (P<0.05)
arterial supply of some AA but did not increase arterio-venous
difference as a percentage of arterial supply (extraction %) and did not
alter milk protein yield. Acivicin decreased (P<0.05) milk protein
yield but this effect was not found when NAC was administered in
combination with acivicin. This indicates that NAC, by indirectly
enhancing intracellular cysteine, countered the effect of acivicin
inhibition, suggesting a role for y-GT in supply of cysteine for
milk protein synthesis.
Keywords: NZSAPAB;
goats; cysteine; amino acid transport; milk protein; acivicin;
N-acetylcysteine
Last Updated 7/08/01
