A model of protein-colloidal gold interactions.

Abstract

We prepared homogeneous populations of colloidal gold particles of various sizes. These were analyzed for size distribution and number of particles per unit volume. On exposure to increasing concentrations of insulin, myoglobin, protein A, peroxidase, serum albumin, galactosylated serum albumin, lactoferrin, transferrin, catalase, low-density lipoprotein, ferritin, and polymeric IgA, protein binding was a saturable process. Using serum albumin, we verified that a reversible equilibrium was reached within 15 minutes. Scatchard analysis of the interactions between all of these proteins and the gold particles resulted in a single component, linear relation. For a given particle size, the number of binding sites for various proteins was inversely proportional to their molecular weight. Conversely, when the size of particles was varied, the number of binding sites was directly proportional to the average area of each gold particle. All results are compatible with a monomolecular shell of protein surrounding the particle at saturation, the binding capacity being inversely proportional to the projection area of the protein. We present direct morphological evidence for this model. The affinity of the various proteins for the colloid also increased with molecular weight, and was not related to the protein isoelectric point. For globular proteins, the monomolecular shell model makes possible prediction of the number of molecules that will saturate a gold particle, if the average diameter of the gold particles and the molecular weight of the protein are known.

Localization of polysaccharides in isolated and intact cuticles of eucalypt, poplar and pear leaves by enzyme-gold labelling

“…Concerning cellulase, 1 ml of the Au solution was mixed with 20 µl of a 0.2% solution of the enzymatic mixture. A 2.5:1 colloidal Au:enzyme ratio was selected for preventing the flocculation of the Au colloid in the final solution [22]. After 5 min stirring of the Au-enzyme solution, 100 µl of 1% polyethylene glycol (PEG, Sigma-Aldrich) were added in order to improve the stability of the Au-enzyme complex and to minimize non-specific enzyme adsorption to the tissues.…”

Expression of a Testis-Specific Nuclear Protein, TRA98, in Mouse Testis during Spermatogenesis. A Quantitative and Qualitative Immunoelectron Microscopy (IEM) Analysis

“…Protein Agold probe (15 nm gold) was prepared following the method of de Roe et al [6]. Rabbit anti-rat IgG was purchased from DAKO (Tokyo, Japan).…”

Ultrastructural analysis of lysosome reactions to inside-out cell membrane vesicles in a cell-free system

“…Bovine serum albumin-coated CG (BSA-CG) and rabbit anti-rat erythrocyte spectrin IgG-coated IM (anti-Sp-IM) were prepared basically according to the methods of de Roe et al 41) and Biéva et al 42) , respectively. Protease inhibitors, leupeptin, pepstatin and chymostatin, were purchased from Peptide Institute Inc. (Osaka, Japan), and aprotinin and phenylmethylsulfonyl fluoride were purchased from Sigma (St. Louis, MO).…”