ISSN:
1399-3054
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Absorption of Amino Acids by Lutoids from the Latex of Hevea brasiliensis.The latex of Hevea brasiliensis is a fluid protoplasm containing organelles with a single membrane that are called lutoids. They are microvacuoles of a lysosomal character. The intact lutoids can easily be isolated in an isotonic medium by the usual procedures of cellular fractionation.Previous studies have shown the existence of a compartmentation of the free amino acids in latex. While acidic components dominate in the cytoplasmic serum, the lutoid serum contains mainly basic components. These findings, as well as the part played by the lutoids in the latex flow and in the process of latex coagulation, led the authors to study the penetration of acidic, neutral and basic amino acids into the lutoids. Labelled amino acids were used for the purpose. Special interest was given to the uptake of lysine, which is transported into the lutoids against a concentration gradient in the absence of a metabolic energy source. The process is linear for at least 30 min and follows Michaelis–Menten kinetics as a function of the lysine concentration. The uptake is strictly temperature and pH dependent. It increases in the presence of ATP. Lysine uptake by lutoids is also increased by application of Ethrel, ethylene generator, to the bark of tapped trees. 2,4-Dinitrophenol (2,4-DNP), ammonium chloride and N-ethylmaleimide (NEM) inhibit the influx. Neutral l-amino acids do not affect the uptake of l-lysine, while l arginine inhibits lysine transport competitively. d-lysine is without effect on l-lysine uptake by lutoids. Under conditions used in this study no lysine efflux is observed. A mechanism governing the penetration of basic amino acids against a concentration gradient is discussed, and the possible role of a proton gradient is suggested.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1399-3054.1977.tb01888.x
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