Is intestinal peptide transport energized by a proton gradient?

Area of Science:

• Physiology
• Biochemistry
• Molecular Biology

Background:

• Intact peptide transport and intracellular hydrolysis are vital for protein digestion product absorption in the mammalian small intestine.
• Previous research suggested active sodium-dependent peptide transport, but recent studies challenge this.
• Peptides, like amino acids, are transported as zwitterions across membranes.

Purpose of the Study:

• To elucidate the mechanism of peptide transport across the intestinal brush-border membrane.
• To determine the role of sodium and proton gradients in peptide absorption.
• To investigate the electrogenic nature of peptide transport.

Main Methods:

• Studies using purified brush-border membrane vesicles.
• Analysis of membrane potential changes during peptide transport.
• Investigation of peptide transport under varying proton gradients and in the presence of ionophores.

Main Results:

• Peptide transport is an electrogenic process, causing membrane depolarization independent of sodium.
• An inward proton gradient significantly stimulates peptide transport.
• Proton ionophores dissipate the proton gradient, reducing peptide transport stimulation.

Conclusions:

• Peptide absorption in the intestine is likely mediated by proton-coupled cotransport.
• The proton gradient, maintained by Na+-H+ exchangers and Na+-K+-ATPase, serves as the in vivo energy source for uphill peptide transport.
• Sodium is indirectly involved in peptide absorption by maintaining the essential proton gradient.