Farm Animal Metabolism and Nutrition

Chapter 1

Amino Acid and Peptide

Transport Systems

J.C. Matthews

Department of Animal Sciences, University of Kentucky,

Lexington, Kentucky, USA

Introduction

All cells require a continuous supply of
amino acids to meet their metabolic
demands. A primary concern of animal
nutritionists is the need to understand what
the capacity for
-amino acid absorption is,
in order that diets can be formulated to
provide adequate, but not excessive, amino
acids for a given production state. The litera-
ture is replete with the characterization of
free and peptide-bound amino acid transport
systems that are expressed by laboratory
animals and humans. By comparison, little
research has been conducted to identify the
presumably analogous transport systems in
farm animal species. Given the economic
importance of these species, and the high
rates of growth and protein production cur-
rently demanded by producers, the lack of
knowledge regarding specific farm animal
transporter physiology may be limiting our
ability to formulate the diets and to design
feeding strategies that optimize protein syn-
thesis and retention. Due to the wealth of
information regarding amino acid and pep-
tide transport systems and proteins being
generated by biomedical research, and the
similarities that appear to exist among

animals species, a unique opportunity exists

to identify and characterize the function of

livestock species-specific free and peptide-

bound amino acid absorption mechanisms.

This chapter begins with a general

discussion of transport protein (transporter)

absorption theory that is germane to amino

acid and peptide absorption, proceeds by

describing the biochemical and molecular

mechanisms that have been characterized

for the transport of free and peptide-bound

amino acids, and concludes with a descrip-

tion of what is known about these processes

in chickens, pigs, sheep and cattle. Unless

noted otherwise, the standard three-letter

abbreviations for amino acids are used for

peptides, and the Lisomer is implied for

both free and peptide-bound amino acids.

Due to the limited number of references

allowed for this chapter, the author

apologizes in advance for his inability to

credit the many researchers who have

contributed to the information presented.

Transporter Theory

Mammals have >100 different types of

cells. Therefore, as might be expected,

© CAB International2000. Farm Animal Metabolism and Nutrition

(ed. J.P.F. D’Mello) 3