Ma. Dudley et al., LACTASE-PHLORHIZIN HYDROLASE TURNOVER IN-VIVO IN WATER-FED AND COLOSTRUM-FED NEWBORN PIGS, Biochemical journal, 320, 1996, pp. 735-743
We have estimated the synthesis rates in vivo of precursor and brush-b
order (BB) polypeptides of lactase phlorhizin hydrolase (LPH) in newbo
rn pigs fed with water or colostrum for 24 h post partum. At the end o
f the feeding period, piglets were anaesthetized and infused intraveno
usly for 3 h with L-[4-H-3]phenylalanine. Blood and jejunal samples we
re collected at timed intervals. The precursor and BB forms of LPH wer
e isolated from jejunal mucosa by immunoprecipitation followed by SDS/
PAGE, and their specific radioactivity in Phe determined. The kinetics
of precursor and BB LPH labelling were analysed by using a linear com
partmental model. Immuno-isolated LPH protein consisted of five polype
ptides [high-mannose LPH precursor (proLPH(h)), complex glycosylated L
PH precursor (proLPH(c)), intermediate complex glycosylated LPH precur
sor (proLPH(i)) and two forms of BB LPH]. The fractional synthesis rat
e (K-s) of proLPH(h) and proLPH(c) (approx. 5%/min) were the same in t
he two groups but the absolute synthesis rate (in arbitrary units, min
(-1)) of proLPH(h) in the colostrum-fed animals was twice that of the
water-fed animals. The K-s values of proLPH, polypeptides were signifi
cantly different (water-fed, 3.89%/min; colostrum-fed, 1.6%/min), but
the absolute synthesis rates did not differ. The K-s of BB LPH was not
different between experimental treatment groups (on average 0.037%/mi
n). However, the proportion of newly synthesized proLPH(h) processed t
o BB LPH was 48% lower in colostrum-fed than in water-fed animals, We
conclude that in neonatal pigs, the ingestion of colostrum stimulates
the synthesis of proLPH(h) but, at least temporarily, disrupts the pro
cessing of proLPH polypeptides to the BB enzyme.