title: Isotopic tracing for calculating the surface density of arginine-glycine-aspartic acid-containing peptide on allogeneic bone.
abstract: OBJECTIVE
  To investigate the feasibility of determining the surface density of arginine-glycine-aspartic acid (RGD) peptides grafted onto allogeneic bone by an isotopic tracing method involving labeling these peptides with (125) I, evaluating the impact of the input concentration of RGD peptides on surface density and establishing the correlation between surface density and their input concentration.
  
  
  METHODS
  A synthetic RGD-containing polypeptide (EPRGDNYR) was labeled with (125) I and its specific radioactivity calculated. Reactive solutions of RGD peptide with radioactive (125) I-RGD as probe with input concentrations of 0.01 mg/mL, 0.10 mg/mL, 0.50 mg/mL, 1.00 mg/mL, 2.00 mg/mL and 4.00 mg/mL were prepared. Using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide as a cross-linking agent, reactions were induced by placing allogeneic bone fragments into reactive solutions of RGD peptide of different input concentrations. On completion of the reactions, the surface densities of RGD peptides grafted onto the allogeneic bone fragments were calculated by evaluating the radioactivity and surface areas of the bone fragments. The impact of input concentration of RGD peptides on surface density was measured and a curve constructed.
  
  
  RESULTS
  Measurements by a radiodensity γ-counter showed that the RGD peptides had been labeled successfully with (125) I. The allogeneic bone fragments were radioactive after the reaction, demonstrating that the RGD peptides had been successfully grafted onto their surfaces. It was also found that with increasing input concentration, the surface density increased.
  
  
  CONCLUSIONS
  It was concluded that the surface density of RGD peptides is quantitatively related to their input concentration. With increasing input concentration, the surface density gradually increases to saturation value.
authors: Department of Bone Oncology, Tianjin Hospital, Tianjin, China.
authors: Xiao-bin
authors: XB
authors: Hou
authors: Yong-cheng
authors: YC
authors: Hu
authors: Jin-quan
authors: JQ
authors: He
mesh_terms: D001842:Bone and Bones / Q000166:cytology*; D003432:Cross-Linking Reagents; D005022:Ethyldimethylaminopropyl Carbodiimide; D005240:Feasibility Studies; D006801:Humans; D007457:Iodine Radioisotopes; D009842:Oligopeptides / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D003432:Cross-Linking Reagents; D007457:Iodine Radioisotopes; D009842:Oligopeptides; C047981:arginyl-glycyl-aspartic acid; D005022:Ethyldimethylaminopropyl Carbodiimide