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H A Saroff

Publications and source records attributed to H A Saroff.

36 records · Page 2Linked to original sources
PubMed1980

An evaluation of the significance of amino acid sequence homologies in human histocompatibility antigens (HLA-A and HLA-B) with immunoglobulins and other proteins, using relatively short sequences.

A computer search was carried out for homologies between HLA-A and HLA-B antigen sequences and the sequences of constant and variable regions of immunoglobulins and of all other sequenced proteins. Searches were made both with relatively short peptide sequences from the HLA antigens and with those longer peptide sequences which were available in 1978. Significant homology of HLA antigen sequences to immunoglobulin constant region sequences was found in two cases: (1) a short decapeptide sequence which includes the fourth cysteine residue of HLA-B7 and (2) an 89-amino-acid residue (Ac-2) C-terminal fragment of the papainsolubilized HLA-B7 molecule. The difficulty of establishing statistically significant sequence homology with relatively short peptide sequences is emphasized by computer-based comparisons of the decapeptide sequence with randomly generated peptide sequences. It is concluded that statistically significant homology with short sequences can be assured only when extraordinarily high degrees of homology are present and additional constraints are included in the matches, for example, matches at relatively rare amino acid residues such as Cys, His and Trp. The homology of the 89-amino-acid residue sequence to constant region sequences of immunoglobulins is as great as or greater than that of beta 2-microglobulin. These findings and the unique domain structure involving a disulphide loop of comparable size strongly favour a common evolutionary origin for this region of HLA-A and -B, beta 2-microglobulin and immunoglobulin constant regions.

Amino Acid Sequence↗
PubMed1975

Ligand-induced self-association of human luteinizing hormone. Negative cooperativity in the binding of 8-anilino-1-naphthalensulfonate.

The self-association of human luteinizing hormone (hLH) is enhanced in the presence of 8-anilino-1-naphthalenesulfonate (ANS). Sedimentation equilibrium measurements indicate that the hormone exists primarily as a dimer in the presence of excess ANS. It is shown that, for a self-associating protein system in which monomer and dimer have different affinities and/or capacities for ligand, both the shape and the position of the binding curve depend on protein concentration. Gel filtration and fluorescence measurements indicate that the hLH dimer has a single high affintiy site (K greater than 10(6) M-1) for ANS while binding to the monomer is too weak to be observed. This leads to negative cooperativity in the binding and to a shift of the binding curve to lower free ligand concentration with increasing concentration of the hormone.

Anilino Naphthalenesulfonates↗
PubMed1975

Ligand-induced self-association of human chorionic gonadotropin. Positive cooperativity in the binding of 8-anilino-1-naphthalenesulfonate.

Human chorionic gonadotropin (hCG) self-associates to form higher molecular weight species in the presence of the fluorescence probe 8-anilino-1-naphthalenesulfonate (ANS). Sedimentation equilibrium and fluorescence titration data have been analyzed in terms of a monomer-dimer-tetramer model in which the various oligomers have different affinities and/or capacities for the ligand. The results indicate that the ligand affinities are in the order tetramer greater than dimer greater than monomer whereas the numbers of ligand binding sites per mole of hCH are in the reverse order. Consequently, addition of ANS first shifts the equilibrium from monomer to tetramer and gives rise to positive cooperativity in the titration curves. At sufficiently high ANS concentration (approximately 0.5 mM), the equilibrium shifts back to the dimer because of its greater binding capacity. This is manifested by a second phase in the titration curve and a decrease in the polarization of ANS fluorescence. The results are discussed in terms of the general problem of ligand controlled protein association and are contrasted to results reported to the previous paper for the homolgous protein, human luteinizing hormone.

Anilino Naphthalenesulfonates↗
PubMed1975

Negative cooperativity in the binding of thyroxine to human serum prealbumin. Preparation of tritium-labeled 8-anilino-1-naphthalenesulfonic acid.

The binding of thyroxine (T4) and 8-anilino-1-naphthalenesulfonic acid (ANS) to human serum prealbumin was measured by equilibrium dialysis at pH 7.4 in 0.05 M phosphate-0.10 M NaCl at 25 degrees. The data were analyzed for the binding constants based on equations for (1) two independent sites and (2) two identical sites with negative interaction. Evaluation by the independent site model gave the following association constants: for T4 binding, KT1 = 1.0 x 10-8 M-1, KT2 = 9.5 x 10-5 M-1; for ANS binding, KA1 = 9.5 x 10-5 M-1, KA2 = 2.1 x 10-5 M-1. The interactive model gave constants kT = 5.5 x 10-7 M-1 and kA = 5.5 x 10-5 M-1. Interaction factors, alpha, defined such that -RT in alpha is the energy of interaction, were: alpha T = 0.041 AND ALPHA A = 0.62 for T4 and ANS, respectively. The "best fit" values for the number of sites were 2.0 and 1.6 for T4 and ANS, respectively. The binding of T4 to human prealbumin was competitive with ANS, and the binding constants evaluated from competition experiments were in agreement with those found for each ligand when studied separately. On the basis of analysis of X-ray data of human prealbumin (Blake et al.) there appear to be two identical T4 sites. It is therefore evident that the binding of T4 represents a case of negative cooperativity which is presumably due to interaction between ligands.

Anilino Naphthalenesulfonates↗
PubMed1972

The Hill plot and the energy of interaction in hemoglobin.

The Hill plot does not independently yield the average free energy of interaction per binding site, as has been proposed by Wyman, but rather the difference between the free energies of interaction on binding the first and last ligands. It is shown that additional data (or assumptions) and a model for cooperative behavior are required to obtain the average free energy of interaction.

Binding Sites↗
PubMed1970

Model for the action of hemoglobin.

A model is developed for hemoglobin which depends on six Bohr groups per tetramer of hemoglobin. These six groups are assumed to be located in six regions between the four subunits of hemoglobin. When the Bohr groups are assumed to be perturbed in an asymmetrical manner on binding oxygen, these groups then generate the cooperative interactions of hemoglobin. This approach makes it possible to explain oxygen binding, the Bohr effect, specific salt effects, and aggregation effects in a unified manner.

Binding Sites↗