Amino acid, accumulation

A rather satisfactory explanation of the irreversibility of amino acid accumulation in yeast cells is that it might result from specific regulatory mechanisms capable of immobilizing the transporters in a closed position. Uptake of amino acids by a number of permeases does indeed appear to be regulated by specific, and possibly allosteric, feedback inhibition. This idea is based on the fact that a number of transport systems seem to be specifically inhibited by their internally accumulated... 

T. Shepherd and H. V. Davies, Effect of exogenous amino acids, glucose and citric-acid on the patterns of short-term amino acid accumulation and loss of amino acids in the root-zone of sand-cultured forage rape (Bras.sica napiis L.). Plant Soil 158 111 (1994). 

Storage conditions and preservation treatments also can affect the free amino acid content. Some authors [242] reported changes in the concentration of free amino acids of broccoli florets stored in air or in controlled atmospheres. Arginine concentration varied greatly during air storage, while y-amino butyric acid, alanine and an unidentified amino acid accumulated in response to low O2 and/or high CO2 treatment. 

Potashner, S.J. Johnstone, R.M. (1971). Cation, gradients, ATP and amino acid accumulation in Ehrlich cells. Biochim. Biophys. Acta 233,91-103. 

Wool, I.G., Castles, J.J., Moyer, A.N. (1965). Regulation of amino acid accumulation in isolated rat diaphragm Effect of puromycin and insulin. Biochim. Biophys. Acta 107,333-345. 

Among other actions, hormones are known to modify the activities of membrane ion transporters and ion channels, affect the membrane potential, and modulate Na+-driven substrate transport (for review see Moule and McGivan, 1990). These actions in turn are expected to modify cell volume. Thus, for example, hormones are now recognized as potent modulators of liver cell volume (Haussinger and Lang, 1992). Whereas anisoosmotic exposure and amino acid accumulation in hepatocytes primarily lead to cell swelling with secondary activation of volume-regulatory ion transporters, hormones primarily affect the activity of these volume-... 

The uptake and accumulation of various amino acids in Lactobacillus arabinosus have been described. Deficiencies of vitamin B6, biotin, and pantothenic acid markedly alter the operation of these transport systems. Accumulation capacity is decreased most severely by a vitamin B6 deficiency. This effect appears to arise indirectly from the synthesis of abnormal cell wall which renders the transport systems unusually sensitive to osmotic factors. Kinetic and osmotic experiments also exclude biotin and pantothenate from direct catalytic involvement in the transport process. Like vitamin B6, they affect uptake indirectly, probably through the metabolism of a structural cell component. The evidence presented supports a concept of pool formation in which free amino acids accumulate in the cell through the intervention of membrane-localized transport catalysts. 

Effect of Cell Wall Synthesis on Amino Acid Accumulation... 

Earlier investigation of environmental factors which modify the accumulation capacity of LB6 cells foreshadowed much of these findings. Specifically, it was observed that conditions which favor cell wall biosynthesis promote a large increase in amino acid accumulation capacity. These observations originated in the initial studies on osmotic protection when it was observed that LB6 cells washed with vitamin B6-... 

The unusual course of amino acid accumulation in biotin- and pantothenate-deficient cells (Figure 3) also has been found to be markedly influenced by sucrose and other osmotic protectants, as well as by acetate. The course of glutamic acid uptake by biotin-deficient cells in the... 

Further support comes from the studies relating cell wall biosynthesis and amino acid accumulation capacity in vitamin B6-deficient cells, since it is difficult to account for these observations without attributing considerable osmotic activity to the accumulated amino acids. Any description of accumulation which invokes amino acid attachment to intracellular binding sites, whose affinity can be reduced by a vitamin B6 deficiency, must account for the stimulation of uptake that accompanies the synthesis of essentially extracellular cell wall material. If the reduction in affinity occurs because the cell interior becomes overhydrated (a reasonable postulate which follows from the osmotic experiments), the beneficial effect of wall synthesis is not readily explicable, since vitamin B6-deficient cells have a swollen appearance which is not significantly altered after wall synthesis has been stimulated. Thus, the existing overhydration within the cell probably is not reversed by this change. In contrast, the deposition of additional wall substance would prevent further unfavorable consequences of swelling such as membrane distention, and, in this way, forestall the premature cessation of amino acid accumulation. 

L-canavanine and L-canaline. Secondary plant substances may evoke particular types of stereotyped insect behavior via actions within the CNS. An excellent example is the work of Kammer, Dahlman, and Rosenthal (40), who observed that injection of adult Manduca sexta with L-canavanine and L-canaline led, within minutes, to sustained flights lasting many hours. The site of action of L-canavanine and L-canaline was believed to be the CNS. This produced continuous motor output, which became less coordinated with time. L-canavanine and L-canaline are two of some 260 non-protein amino acids accumulated by various plants (41). If an unadapted insect acquired... 

The process of amino acid accumulation is catalyzed by at least five different Na, amino acid-symporters transporting (i) asparagine and glutamine, (ii) arginine, lysine and histidine, (iii) alanine, glycine, serine and threonine, (iv) valine, leucine, isoleucine and methionine and (v) phenylalanine, tyrosine and tryptophane. One more symporter seems to be involved in the uptake of glutamate and aspartate. Cysteine is not transported and inhibits the transport of other amino acids (reviewed in [30]). 

These variations in behavior indicate that harvesting melons at different stages of maturity causes subsequent biochemical events involved in amino acid accumulation to follow markedly different pathways. Recent work shows that melon fhiit harvested up to ten days before commercial maturity exhibits climacteric behavior with respect to ethylene production showing that at least this aspect of ripening is not completely inhibited by premature separation from the plant(P). However, the amount of ethylene produced is dependent on maturity at harvest and fruit harvested five days prematurely generated only about half of the amount of ethylene produced by fruit harvested two days before maturity. Also the lag time required to initiate ethylene production after harvest depended on maturity and was longer for prematurely harvested fruit. Changes in the content of the phytohormone abscisic acid were also correlated with that of ethylene. However whether the different maturity related metabolic responses observed above result from the action of these or other plant hormones awaits further study. 

Amino acid absorption in adult cestodes occurs through multiple carriers that are saturable and sensitive to temperature and to a variety of inhibitors (2,13). Amino acid accumulation typically occurs against steep concentration gradients (16), and the amino acid carrier systems in cestodes seem to be similar to those in mammals. There are separate carriers for acidic and basic amino acids and multiple carriers for the neutral amino acids, which overlap in their specificities. Unlike mammals, however, which show higher affinities for L-amino acids, cestode transporters are not stereoselective. Also,... 

Hickey, M. W., van Leeuwen, H., Hiliier, A. J., and Jago, G. R. (1983b). Amino acid accumulation in Cheddar cheese manufactured from normal and ultrafiltered milk. Aust. J. Dairy Technol. 38, 110-113. 

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