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

摘要

pWe have estimated the synthesis rates iin vivo/i of precursor and brush-border (BB) polypeptides of lactase phlorhizin hydrolase (LPH) in newborn pigs fed with water or colostrum for 24 h ipost partum/i. At the end of the feeding period, piglets were anaesthetized and infused intravenously for 3 h with l-[4-sup3/supH]-phenylalanine. Blood and jejunal samples were collected at timed intervals. The precursor and BB forms of LPH were 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 compartmental model. Immunoisolated LPH protein consisted of five polypeptides [high-mannose LPH precursor (proLPHsubh/sub), complex glycosylated LPH precursor (proLPHsubc/sub), intermediate complex glycosylated LPH precursor (proLPHsubi/sub) and two forms of BB LPH]. The fractional synthesis rate (iK/isubs/sub) of proLPHsubh/sub and proLPHsubc/sub (approx. 5%/min) were the same in the two groups but the absolute synthesis rate (in arbitrary units, minsup-1/sup) of proLPHsubh/sub in the colostrum-fed animals was twice that of the water-fed animals. The iK/isubs/sub values of proLPHsubi/sub polypeptides were significantly different (water-fed, 3.89%/min; colostrum-fed, 1.6%/min), but the absolute synthesis rates did not differ. The iK/isubs/sub of BB LPH was not different between experimental treatment groups (on average 0.037%/min). However, the proportion of newly synthesized proLPHsubh/sub 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 proLPHsubh/sub but, at least temporarily, disrupts the processing of proLPH polypeptides to the BB enzyme./p