alpha 2 Macroglobulin binding to the plasma membrane of cultured fibroblasts. Diffuse binding followed by clustering in coated regions.

Using transmission electron microscopy, we have studied the interaction of alpha 2 macroglobulin (alpha 2 M) with the surface of cultured fibroblasts. When cells were incubated for 2 h at 4 degrees C with ferritin-conjugated alpha 2 M, approximately 90% of the alpha 2 M was diffusely distributed on the cell surface, and the other 10% was concentrated in "coated" pits. A pattern of diffuse labeling with some clustering in "coated" pits was also obtained when cells were incubated for 5 min at 4 degrees C with alpha 2 M, fixed with glutaraldehyde, and the alpha 2 M was localized with affinity-purified, peroxidase-labeled antibody to alpha 2 M.

Cyclized dipeptide model for a beta-bend.

A cyclic dipeptide in which L-Ala-Gly was cyclized with epsilon-aminocaproic acid has been synthesized as a model for a beta-bend. Its conformational properties have been examined by means of conformational energy calculations and nuclear magnetic resonance, infrared, Raman, and circular dichroism spectroscopy in various solvents. These calculations and experiments suggest that a type II beta-bend exists in the Ala-Glymoiety, with an NH.

Collection of insulin, EGF and alpha2-macroglobulin in the same patches on the surface of cultured fibroblasts and common internalization.

We have used video intensification microscopy to observe fluorescent derivatives of insulin, epidermal growth factor and alpha2-macroglobulin added to Swiss 3T3-4 cells. At 4 degrees C, each of these polypeptides binds diffusely to specific receptors on the cell surface. When the cells are warmed to 23 or 37 degrees C, the bound insulin epidermal growth factor or alpha2-macroglobulin rapidly forms patches on the cell surface and is internalized.

A Raman spectroscopic investigation of the disulfide conformation in oxytocin and lysine vasopressin.

The conformation of the CCSSCC moiety in oxytocin and lysine vasopressin is investigated using laser Raman spectroscopy. The Raman spectra of solutions of these hormones in water and in dimethyl sulfoxide show an intense band at 508 cm-1 which is assigned to the S-S stretching mode. The presence of shoulders on this band between 490 and 525 cm-1 shows that there is an equilibrium among several conformations for the disulfide unit of these hormones in solution.

Status of empirical methods for the prediction of protein backbone topography.

An empirical preduction algorithm which uses information on the shrs on either side) interactions in 20 proteins to assign every residue in a protein to one of five conformational states is described. The conformational states are defined in terms of the backbone dihedral angles of the residue so that the prediction algorithm can be used to generate starting conformations for subsequent energy-minimization procedures, which would be necessary to predict the three-dimensional structure of a protein. An estimate is made of the statistical error in the determination of the parameter- describing the effects of short-range and medium-range interactions in proteins, and it is shown that this statistical error plays a large role in limiting the accuracy of all prediture.

The effect of neighboring charges on the helix forming ability of charged amino acids in proteins.

It has been found that the fraction of glutamic acid residues which are helical in proteins is larger than might be expected from the experimentally determined value of the helical stability constants of glutamic acid. In order to understand this difference, the effect of neighboring charged side chains on the glutamic acid residues in proteins of known structure is examined. It is found that a positively charged side chain four residues away from a glutamic acid greatly enhances its probability to be helical.

Helix-coil stability constants for the naturally occurring amino acids in water. IX. Glutamic acid parameters from random poly(hydroxybutylglutamine-co-L-glutamic acid).

The synthesis and characterization of water-soluble random copolymers containing L-glutamic acid with N5-(4-hydroxybutyl)-L-glutamine and the thermally induced helix-coil transitions of these copolymers in water and in 0.1 N KCl are described. The incorporation of L-glutamic acid was found to increase the helix content of the polymer at low pH and to decrease it at high pH even though the presence of 0.