Intestinal transport of amino acids studied in vitro with l-[131I]monoiodotyrosine

Absorption of protein digestion products: a review.

“…Figure 5 is analogous to the Lineweaver-Burk plot of enzyme kinetics, and this linear relationship has been taken to mean that the transport process conforms to the Michaelis-Menten kinetics of enzyme reactions. Kinetics of this type, which have now been shown for a number of L-amino acids and two D-amino acids (e.g., Jervis and Smyth, 1959a;Finch and Hird, 1960b;Nathans et al, 1960;Spencer and Samiy, 1961;Lin et al, 1962;Matthews and Laster, 1965a), are to be expected if the rate-limiting step in transport is combination with or adsorption to some com- Wilson and Wiseman, 1954;Jervis and Smyth, 1960). There remains, however, a possibility that the mechanisms affected are not in fact directly concerned in supplying energy for transport but serve primarily to maintain the integrity of the cell membrane, without which the transport process cannot operate (Finch and Hird, 1960a;Newey and Smyth, 1962).…”

“…Low concentrations of potassium have no effect (at least on monoiodotyrosine transport) but high concentrations are inhibitory, and the inhibition appears to be competitive. Alterations in calcium concentration have no effect (Nathans et al, 1960;Csaky, 1961;Harrison and Harrison, 1963).…”

“…Hagihira, Ogata, Takedatsu, andSpencer and Samiy, 1961), and that those with long side-chains are the most powerful inhibitors of the transport of other amino-acids within this group. The longer the side-chain, the more powerful the inhibiting effect, i.e., the greater the apparent affinity for the common transport mechanism (Finch and Hird, 1960b;Nathans, Tapley, and Ross, 1960;Matthews and Laster, 1965b). It also appears that there are several intestinal transport mechanisms for different groups of amino-acids, there being competition among the members of each group, but not between the members of different groups:…”

“…pH The optimal pH for transport of monoiodotyrosine by rat small intestine in vitro is about 6 (Nathans et al, 1960).…”

“…Christensen et al (1954) suggested that in tissue cells, amino-acid transport might be linked with, and perhaps driven by, potassium transport. A raised potassium concentration acts like a competitive inhibitor of amino-acid transport (Nathans et al, 1960) which suggests that the two transports are also associated in some way in the intestine. The abolition of the transport of both glucose and amino-acids by low sodium concentrations may be the result of interference with a common energy supply to the two mechanisms.…”