title: Endogenous proteins in terminal ileal digesta of adult subjects fed a casein-based diet.
abstract: BACKGROUND
  Although there are several published estimates of the endogenous amino acid composition of ileal digesta in humans, to our knowledge, there are no systematic studies of ileal digesta endogenous proteins.
  
  
  OBJECTIVE
  We determined the nature and composition of endogenous nitrogen-containing substances lost from the upper digestive tract of humans.
  
  
  METHODS
  Digesta were collected from the terminal ileum for a period of 8 h by using a nasoileal tube in 6 adult subjects fed a single meal that contained 22% of casein as the only source of nitrogen.
  
  
  RESULTS
  The total nitrogen that passed the terminal ileum was 39.3 mg/g native digesta dry matter. Of this amount, 86% was proteinaceous, ~60% was bacterial protein, ~7% was soluble-free protein, ~15% was mucin protein, and ~5% was protein from intact mucosal cells. For nonprotein nitrogen, ~5% of the total nitrogen was ammonia, and ~4% of the total nitrogen was urea. Bacterial and human mucosal cellular DNA nitrogen were collectively ~0.5% of the total nitrogen. Approximately 30% of the nonprotein nitrogen (4% of the total nitrogen) remained unidentified. This amount was assumed to include free amino acids, RNAs, amines, and the tetrapyrroles bilirubin and biliverdin. Bacterial nitrogen, combined with ammonia and urea nitrogen, represented >68% of total ileal nitrogenous losses.
  
  
  CONCLUSIONS
  Findings are presented on the endogenous nitrogen-containing compounds that left the terminal ileum. Of particular significance is the observation that mucin was the most abundant truly endogenous component within the terminal ileal digesta. Bacterial protein, which was strictly nondietary rather than endogenous, contributed the highest proportion, by far, of nondietary protein, the result of which makes a significant contribution to published estimates of ileal endogenous amino acids and protein. The high concentration of bacterial protein and the presence of ammonia and urea nitrogen indicate potentially substantial microbial activity within the human distal small intestine.
authors: Riddet Institute, Massey University, Palmerston North, New Zealand.
authors: Warren
authors: W
authors: Miner-Williams
authors: Amélie
authors: A
authors: Deglaire
authors: Robert
authors: R
authors: Benamouzig
authors: Malcolm F
authors: MF
authors: Fuller
authors: Daniel
authors: D
authors: Tomé
authors: Paul J
authors: PJ
authors: Moughan
mesh_terms: D000328:Adult; D000465:Algorithms; D000641:Ammonia / Q000032:analysis; D001426:Bacterial Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D002364:Caseins / Q000008:administration & dosage*; D004247:DNA / Q000032:analysis; D004063:Digestion; D005260:Female; D005752:Gastric Mucins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D005766:Gastrointestinal Contents / Q000737:chemistry*; D006801:Humans; D007082:Ileum / Q000166:cytology / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism; D008297:Male; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism; D010446:Peptide Fragments / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D019518:Postprandial Period; D011506:Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D012995:Solubility; D014508:Urea / Q000032:analysis
chemical_list: D001426:Bacterial Proteins; D002364:Caseins; D005752:Gastric Mucins; D010446:Peptide Fragments; D011506:Proteins; D000641:Ammonia; D014508:Urea; D004247:DNA; D009584:Nitrogen