Human Blood Platelets Accumulate Radioactivity from the Dipeptides ¹⁴C-glycylglycine and ¹⁴C-glycylproline

Summary

Human blood platelets were suspended in plasma or Krebs solution and incubated with radiolabeled glycylglycine or glycylproline in order to study cellular uptake. Platelets accumulated radioactivity against a concentration gradient. In the case of glycylglycine, uptake was not inhibited by cold, or metabolic inhibitors. Uptake of radioactivity derived from glycylglycine or glycylproline did not appear to involve saturable mechanisms since the platelet content of radioactivity was directly related to medium concentration even at high concentrations.

Chromatographic identification of radioactivity in cells and incubation media showed the glycylglycine was not extensively hydrolysed; 80 per cent of platelet radioactivity was intact dipeptide. With glycylproline, cellular radioactivity was entirely ¹⁴C-glycine. There was no direct evidence that this dipeptide actually entered the cells, and we could not determine whether entry did occur with subsequent hydrolysis, or whether hydrolysis preceded uptake.

^* Present address: MRC Clinical Pharmacology Unit and University Department of Clinical Pharmacology, Radcliffe Infirmary, Oxford OX2 6HE, England.

• References

• 1 Adams E, McFadden M, Smith E. L. Peptidases of erythrocytes. I. Distri-bution in man and other species. Journal of Biological Chemistry 1952; 198: 663
• 2 Addison J. M, Burston D, Matthews D. M. Evidence for active transport of the dipeptide glycylsarcosine by hamster jejunum in vitro. Clinical Science 1972; 43: 907
• 3 Adibi S. A. Intestinal absorption of dipeptides in man: relative importance of hydrolysis and intact absorption. Journal of Clinical Investigation 1971; 50: 2266
• 4 Barber A. J, Jamieson G. A. Isolation and characterization of plasma membranes from human blood platelets. Journal of Biological Chemistry 1970; 245: 6357
• 5 Boullin D. J. The action of extracellular cations on the release of the sympathetic transmitter from peripheral nerves. Journal of Physiology 1967; 189: 85
• 6 Boullin D. J, Green A. R. Mechanisms by which human blood platelets accumulate glycine. GABA and amino acid precursors of putative neurotransmitters. British Journal of Pharmacology 1972; 45: 83
• 7 Boullin D. J, Green A. R, Price K. S. The mechanism of adenosine diphosphate induced platelet aggregation: binding to platelet receptors and inhibition of binding and aggregation by prostaglandin E₁ . Journal of Physiology 1972; 221: 415
• 8 Boullin D. J, O’Brien R. A. The accumulation of guanethidine by human blood platelets. British Journal of Pharmacology 1969; 35: 90
• 9 Boullin D. J, Votavova M, Green A. R. Protein synthesis by human blood platelets after accumulation of leucine and arginine. Thrombosis et Diathesis Haemorrhagica 1972; 28: 54
• 10 Boullin D. J, Crampton R. A, Heading C. E, Pelling D. Intestinal absorption in vivo of dipeptides containg glycine, phenylalanine, proline and ß-alanine or histidine in the rat. Clinical Science and Molecular Medicine 1973; 45: 849
• 11 Brock T. D, Wooley S. O. Glycylglycine uptake in streptococci and a possible role of peptides in amino acid transport. Archives of Biochemistry and Biophysics 1964; 105: 51
• 12 Cheeseman C. I, Smyth D. H. Specific transfer process for intestinal ab-sorption of peptides. Journal of Physiology 1973; 229: 45
• 13 Cutler R. W. P, Hammerstad J. P, Cornick L. R, Murray J. E. Efflux of amino acid neurotransmitters from rat spinal cord slices 1. Factors influencing the spontaneous efflux of ¹⁴C-glycine and ³H-GABA. Brain Research 1971; 35: 337
• 14 Eavenson E, Christensen H. N. Transport systems for neutral amino acids in the pigeon erythrocyte. Journal of Biological Chemistry 1967; 242: 5386
• 15 Ferreira S. H, Vane J. R. Half-lives of peptides and amines in the circulation. Nature, London 1967; 215: 1237
• 16 Heuckel H. J, Rogers Q. R. Prolylhydroxyproline absorption in hamsters. Canadian Journal of Biochemistry and Physiology 1972; 50: 782
• 17 Kessel D, Lubin M. On the distinction between peptidase activity and peptide transport. Biochimica Biophysica Acta 1963; 71: 656
• 18 Leach F. R, Snell E. E. The absorption of glycine and alanine and their peptides by Lactobacillus-casei. Journal of Biological Chemistry 1960; 235: 3523
• 19 Marks N. Peptide hydrolases. In: Handbook of Neurochemistry Vol 3. Metabolic reactions in the nervous system. Edited by Abel Lajtha Plenum Press; New York & London: 1970: 133
• 20 Peters T. J. The subcellular localization of di- and tripeptide hydrolase activity in guinea-pig small intestine. Biochemical Journal 1970; 120: 198
• 21 Peters T. J, MacMahon M. T. The absorption of glycine and glycine oligopeptides by the rat. Clinical Science 1970; 39: 811
• 22 Peters T. J, Modha K, MacMahon M. T. The digestion and absorption of glycine oligopeptides. Gut 1969; 10: 1055
• 23 Rubino A, Field M, Shwachman H. Intestinal transport of amino acid residues of dipeptides, 1. Influx of the glycine residue of glycyl-L-proline across mucosal border. Journal of Biological Chemistry 1971; 246: 3542
• 24 Simmonds S. The role of dipeptidases in cells of Escherichia coli strain K-12. Journal of Biological Chemistry 1966; 241: 2502
• 25 Simmonds S, Toye N. Peptidases in spheroplasts of Escherichia coli K-12. Journal of Biological Chemistry 1966; 241: 3852
• 26 Vidaver G. A. Transport of glycine by pigeon red cells. Biochemistry, N. Y 1964; 3: 662
• 27 Zieve P. D, Solomon H. M. Uptake of amino acids by the human platelet. American Journal of Physiology 1968; 214: 58