Lactase phlorhizin hydrolase turnover in vivo in water-fed and colostrum-fed newborn pigs

摘要

We have estimated the synthesis rates in vivo of precursor and brush-border (BB) polypeptides of lactase phlorhizin hydiolase (LPH) in newborn pigs fed with water or colostrum for 24 h post partum At the end of the feeding period, piglets were anaesthetized and infused intravenously for 3 h with L-[4-~3H]-phenylalanine. Blood and jejunal samples were collected at timed intervals. The precursor and BB fbims of LPH were isolated from jejunal mucosa by immunoprecipitation followed by SDS/PAGE, and theirspecific radioactivity in Phe determined. The kinetics of precursor and BB LPH labelling were analysed by using a linear compartmental model Immuno-isolated LPH protein consisted of five polypeptides [high-man-nose LPH precursor (proLPH_h), complex glycosylated LPH precursor (proLPH_c), intermediate complex glycosylated LPH precursor (proLPH_i) and two forms of BB LPH], The fractional synthesis rate (K_s) of proLPH_b and proLPH_c (approx. 5 %/ min) were the same in the 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, poiypeptides were significantly 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 %/min). However, the proportion of newly synthesized proLPH_h processed to 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 processing of proLPH polypeptides to the BB enzyme.