Characterization of a novel variant of amino acid transport system asc in erythrocytes from Przewalski’s horse (Equus przewalskii).

This study explores the amino acid transport system, specifically the asc1-type transport system, in the red blood cells of several species of wild horses and zebras. The researchers discovered a new variant with a high affinity for the amino acid L-lysine in Przewalski’s horse. Unlike zebras, Przewalski’s horse red blood cells showed consistently high rates of L-alanine uptake, suggesting unique differences in the transport mechanisms across different species.

Key Findings

• The research focused on the asc1-type transport system, responsible for transporting amino acids into cells, in the red blood cells of different wild horse species: Przewalski’s horse, Hartmann’s zebra, Grevy’s zebra, and onager.
• In particular, the Przewalski’s horse showed uniformly high rates of an amino acid called L-alanine uptake, mediated by the asc1-type transport system, which means it was efficient in transporting L-alanine to the blood cells.
• Notably, the Przewalski’s horse asc1 isoform showed a significantly higher affinity (6.4 times more) for another amino acid, L-lysine, than its thoroughbred counterpart. This high affinity for L-lysine demonstrates functional and possibly structural similarities between asc and the classical Na(+)-dependent system ASC, and the Na(+)-independent dibasic amino acid transport system y+.
• However, the rate of L-alanine uptake in the red blood cells of the zebra species showed variety, indicating differences in their transport mechanisms compared to the Przewalski’s horse.

Methodology

• The study involved an examination of the L-alanine amino acid uptake in red blood cells from 10 individual Przewalski’s horses. The uptake rate was measured at 37 degrees Celsius, a standard body temperature for mammals.
• They then performed similar tests on different species of wild zebras and onagers, at the same temperature, for comparison.
• Using radiation inactivation analysis, they estimated the target size of the asc transporter in Przewalski’s horse red blood cells, obtaining an in situ apparent molecular weight of 158,000 +/- 2500 (SE).

Implications

• The high apparent affinity exhibited by the Przewalski’s horse for the transport of L-lysine is a key discovery as it suggests a unique variant of the asc1-type transport system that could be structurally and functionally similar to other established transport systems.
• This finding could potentially bring about a greater understanding of the sophisticated control of amino acid transport in different species, and how such mechanisms have evolved and diversified in different equine populations to facilitate their particular needs or environments.