Suckling Rat Colon Synthesizes and Processes Active Lactase-Phlorizin Hydrolase Immunologically Identical to that from Jejunum

Abstract

ABSTRACT. To identify potential tissue-specific characteristics of intestinal glycoprotein synthesis and processing, rat intestinal lactase-phlorizin hydrolase (L-Ph) was studied after pulse-labeling of colonic explants from 5-d-old suckling rats in organ culture and the data compared to similar studies in rat jejunum. Histologic sections of 5-dold proximal colon showed villus-like structures lined with columnar epithelial cells. Lactase and phlorizin hydrolase activities showed tissue-specific developmental patterns. Using a MAb to small intestinal L-Ph, we were able to immunoprecipitate from colon at different ages a protein that hydrolyzed lactose and phlorizin, and whose activity was not inhibited by p-chloromercuribenzoate. After pulselabeling for 60 min and chase for 30 min, immunoprecipitated L-Ph from total homogenates of rat colonic explants appeared on fluorography of SDS-PAGE as one band of approximately 205 kD. With increasing time of chase, it took 240 min before the precursor form was converted to the intermediate form (equivalent to the 180-kD form in jejunum) and the mature form (equivalent to the 130-kD form in jejunum), although these conversions in the jejunum were observed within 60 min of chase, and only 30 min of pulse labeling. When compared on SDS-PAGE to immunoprecipitated jejunal L-Ph, the precursor form in the colon had a slightly higher apparent mol wt than the corresponding precursor form found in the endoplasmic reticulum-Golgi fraction of the jejunum. The intermediate as well as the mature L-Ph forms in the colon were also both somewhat higher in apparent molecular weight than the same bands in the microvillus membrane fraction from jejunal explants. Removal of N-linked oligosaccharides from jejunum and colonic forms of L-Ph produced bands on SDS-PAGE with identical mobility, suggesting that the proteins were the same. The data demonstrate that, in neonatal colon, enzymatically active L-Ph undergoes biosynthetic and processing events similar to those in the jejunum. During early life, colonic L-Ph may function in the salvage of lactose not absorbed in the small intestine. Lactase-phlorizin hydrolase is a major intestinal hydrolytic enzyme of particular importance in early life of most mammals, and is found chiefly in the jejunum, although extensive studies on potential other localization beyond the small intestine are lacking. Most biochemical studies of microvillar hydrolases have focused on the small intestine, and comparatively little is known about differentiation of specific enzymes in the colon. The adult colon functions primarily in the regulation of salt and water transport and bacterial fermentation. The fetal and newborn colon, however, differs considerably in morphology and probably function from that of the adult. In the rat fetus, the proximal colon is populated by villi and microvilli after the formation of the gut lumen and retains this form until 10 days after birth (1,The most extensive developmental studies of the morphology and enzyme patterns of the colonic epit...

Fetal endoderm primarily holds the temporal and positional information required for mammalian intestinal development.

“…This may correspond to an intracellular accumulation of the protein linked to a delayed processing of the lactase precursor. In rat neonates a delayed processing occurs in colonocytes compared with enterocytes (Bfiller et al, 1989;Freund et al, 1990).…”

Expression of Human Intestinal mRNA Transcripts during Development: Analysis by a Semiquantitative RNA Polymerase Chain Reaction Method

“…Analysis of the mRNA expression in the colon was of particular interest in view of the many reports concerning changes in the expression of these genes in colon cancer (26)(27)(28)(29) and the known transient expression of certain enterocytic markers in fetal colon (30)(31)(32)(33). Because the colon-specific transcript of carbonic anhydrase 1 (EC 4.2.1.1) is one of the very few colon-specific markers available (34), it was of interest to compare the expression of this mRNA with those of the brush-border proteins.…”

20 Years of Scientific Training of Dutch Medical Students in an American Academic Division for Pediatric Gastroenterology and Nutrition: Impact on Career Development

“…Twenty‐five (64%) of the students contributed to 1 or more scientific manuscripts directly based on the topic of their research in Boston. The first publication related to this program dates back to 1989 (4). Individual candidates reported a total of 46 PubMed citations.…”