Leon E. Rosenberg

Transport of amino acids by slices of rat-kidney cortex

Abstract This report presents data showing that α-aminoisobutyric acid, glycine, L -phenylalanine, and L -histidine are accumulated against a concentration gradient by slices of rat-kidney cortex in vitro . The process(es) involved depend on oxidative metabolism as shown by inhibition when anaerobic conditions or 2,4-dinitrophenol are substituted for the basal system described. The rate and extent of transport have been shown to depend on the initial concentration of the amino acids studied. The potential value of and hazards inherent in the technique are described and relationship to renal tubular transport of amino acids in the intact animal discussed.

Studies of the kinetics of amino acid transport, incorporation into protein and oxidation in kidney-cortex slices

Abstract The present report describes an approach to the study of the steady-state kinetics of amino acid transport and protein synthesis in rat-kidney-cortex slices, using multi-compartment models. The following conclusions seem justified from the data presented: 1. 1. Using inulin and the non-metabolizable amino acid, α-aminoisobutyric acid, amino acid uptake could be characterized by a three-compartment “parallel” model representing the medium, extracellular space and intracellular space. Appropriate influx and efflux rate constants were calculated. 2. 2. 2,4-Dinitrophenol and incubation at 27° significantly effected the rate of efflux of α-aminoisobutyric acid from the intracellular space, as well as the rate of influx, suggesting that efflux phenomena are metabolically linked. 3. 3. Kinetic studies of combined transport and protein synthesis with glycine and l -lysine indicated that equilibration of exogenous amino acid with the intracellular pool need not occur before incorporation into protein takes place. 4. 4. The kinetics of 14 CO 2 evolution from labeled l -lysine indicated that the rate of amino acid oxidation reflected the buildup of the intracellular lysine pool. 5. 5. The results suggest that the mathematical approach, used in the analysis of the experimental data, provides means of quantitating and understanding membrane phenomena and the relationship between rates of membrane transfer and subsequent intracellular utilization.

The role of sodium ion in the transport of amino acids by the intestine.

Abstract 1. 1. Decreasing the incubation medium Na+ concentration below physiologic levels resulted in decreased transport of Na+ and water in the isolated rabbit jejunum as well as diminution of amino acid transport. 2. 2. Ouabain inhibited the transport of Na+ and amino acids in everted jejunal sacs. 3. 3. Reduction of medium Na+ was associated with decreased tissue Na+ and K+ content while ouabain produced elevated tissue Na+ and reduced tissue K+ concentrations. 4. 4. Kinetic analysis of amino acid-uptake data showed that ouabain and reduction of medium Na+ caused a slowing of both influx and, to a lesser degree, efflux coefficients. 5. 5. The Na+ ion was shown to affect energy-independent (diffusion) as well as energy-dependent (active) transport of amino acids.

Hexose inhibition of amino acid uptake in the rat-kidney-cortex slice

Abstract Glucose, galactose and fructose have been shown to inhibit the intracellular accumulation of amino acids by the rat-kidney-cortex slice. The uptake of glycine, α-amino- [1−14C]isobutyric acid, valine and cycloleucine was inhibited by these hexoses but the accumulation of lysine, histidine and phenylalanine was unaffected. The inhibitory effect has been shown to be dependent upon the length of incubation and upon the sugar concentration. Evidence has been presented to indicate that sugars reduce the rate of influx of amino acid into cells but have no effect upon the apparent affinity of transport sites for amino acids.

The effect of high galactose diets on urinary excretion of amino acids in the rat

Young, male, Sprague-Dawley rats, maintained on 30% galactose diets for 50–90 days developed amino aciduria and polyuria. No disturbance of plasma amino acid concentration was noted suggesting that the amino aciduria was related to defective renal tubular reabsorption of amino acids. Chromatographic analysis of the urinary amino acids revealed increases in taurine, aspartic acid, glutamic acid, alanine, β-alanine and ethanolamine. Studies using [14C]glucose failed to demonstrated any inhibition of the hexose monophosphate shunt pathway in the kidneys of the galactose fed animals.

Compartmental analysis of collagen synthesis in fetal rat calvaria: I. Perturbations of proline transport

Abstract We formulated a mathematical model with steady state and nonsteady state features for describing proline uptake and utilization in fetal rat calvaria. Conclusions based on our model include the following: 1. 1. Proline entering the cell first passes through a protein precursor pool from which protein synthesis originates. 2. 2. Rates of proline influx control the size of this precursor pool. 3. 3. Proline influx, efflux, and incorporation of proline into protein are related by saturable mechanisms to proline concentration in their respective pools of origin. 4. 4. Amino acids which are not incorporated into protein can inhibit proline incorporation into protein as well as proline transport.

The effect of phlorizin on amino acid transport in rat-kidney-cortex slices

Abstract Phlorizin has been shown to enhance the accumulation of amino acids by the rat-kidney-cortex slice. Evidence has been presented that this drug has no effect on the affinity of the carrier site(s) for amino acids but inhibits the efflux of amino acid from the intracellular fluid, possibly by increasing the intracellular binding of amino acids. Phlorizin was found to diminish the incorporation of amino acids into protein and to cause an increased oxidation of amino acids.

Pathologic Aminoaciduria in Experimental Ascorbic Acid Deficiency

Summary Ascorbic acid deficiency in the guinea pig is associated with prominent aminoaciduria, due largely to excessive glycine excretion. Pair-feeding studies indicate that this aminoaciduria results from ascorbic acid depletion per se, and cannot be attributed to starvation or weight loss. It is concluded that experimental scurvy provides a suitable model for future in vivo or in vitro studies of amino acid transport.