Molecule--receptor specificity.

The specificity of binding between small molecules and macromolecular receptors may be studied by comparing theoretically calculated conformational potential energy surfaces of a series of chemically similar molecules which have a range of receptor binding energies and biological activities. In this way essential requirements for binding may be highlighted, including the necessity of the small molecule adopting, or passing through, conformations which are not at energy minima and not found either in the solid state or in aqueous solution. In particular the conformational demands of the adrenergic beta-receptor and histamine H1 receptor are considered.     

Comparative specificity of microbial acid proteinases for synthetic peptides. I. Primary specificity

The specificity of various acid proteinases from mold and yeast such as Aspergillus niger, Aspergillus saitoi, Rhizopus chinensis, Mucor miehei, Rhodotorula glutinis, and Cladosporium sp. were comparatively determined using with

(X = various amino acid residues) as substrates. Pepsin was used in a comparative study. Since the peptides were susceptible to these enzymes at the peptide bonds indicated by the arrows, except for the ones from both Aspergillus species and Rhodotorula, we could examine their specificity with respect to the amino acid residue on both sides of the splitting point. The results indicated that the microbial enzymes were specific for aromatic, or bulky and hydrophobic amino acid residues on both sides, as had been observed with pepsin. The specificity of the enzymes from Aspergillus and Rhodotorula was not determined because of lack of hydrolysis of the peptides.     

Mutagenic specificity in reovirus.

Mutagenic specificity in response to chemical mutagens has been observed with certain temperature-sensitive mutants of reovirus type 3. One mutant induced by nitrous acid reverted specifically with nitrous acid. Three nitrosoguanidine-induced mutants reverted after nitrous acid treatment. These findings thus suggest that analysis of chemical induction of reversion from the temperature-sensitive phenotype may be a useful approach for studying the nature of mutation in animal viruses.     

Dynamic aspects of enzyme specificity.

There are two aspects of enzyme specificity: recognition of the substrate by the formation of an enzyme-substrate compound and recognition of the transition state by catalysis of the reaction. Kinetic studies with inactive substrate analogues as potential competitive inhibitors, and structural studies of their compounds with enzymes, give information about the first of these specificity elements. Comparative kinetic studies with alternative substrates give information about both. There is a great deal of information from kinetic studies of dehydrogenases about the coenzyme specificities, substrate specificities and stereospecificities and mechanisms of these enzymes, particularly alcohol dehydrogenases. Recent X-ray diffraction studies of dehydrogenases have given insight into the molecular basis of some of their specificity elements. An attempt is made to correlate the available kinetic and structural data for alcohol and lactate dehydrogenases.     

Engineering T lymphocyte antigen specificity.

Targeting of immune cells by bispecific antibodies has proven to be a powerful tool for the investigation of cellular cytotoxicity, lymphocyte activation and induction of cytokine production, as well as to represent an innovative form of immunotherapy for the treatment of cancer. The hallmark of this approach is the use of the specificity of monoclonal antibodies to join target and immune cells by virtue of the dual specificity of bispecific antibodies for the two entities. More precisely, the bispecific antibody has two different binding sites, which are capable of recognizing tumor associated antigens on the one hand and lymphocyte activation sites on the other. This process of crosslinking results in the activation of the lymphocyte and triggering of its lytic machinery, as well as lymphokine production. A major advantage of this therapeutic modality is, that use is made of the normal cellular immune defence system and therefore is only associated with minor toxicity. The distinct lymphocyte populations, which can be used for adoptive immunotherapy and the various bispecific antibody preparations, as well as the chimeric immunoglobulin/T cell receptor construction, are the major topics of this review.     

Substrate specificity of human alpha-L-fucosidase.

Human α-l-fucosidase is a soluble lysosomal enzyme which hydrolyzes α-l-fucose residues linked to the 2 position of galactose or the 3, 4, or 6 position ofN-acetylglucosamine. Demonstration of activity towards natural oligosaccharide or glycosphingolipid substrates was achieved by measuring liberated l-fucose by coupling to fucose dehydrogenase and NAD and measuring NADH production spectrophotometrically. Activity of purified human spleen, brain, and cultured skin fibroblast or crude cell extracts towards 4-methylumbelliferyl-α-l-fucoside had a pH optimum of 4.5 to 5.5 and was unaffected by the presence of neutral detergents such as Triton X-100. However, the addition of sodium taurocholate or other bile salts to the incubation mixture caused a marked inhibition at pH 5 and a shift in pH optimum to the pH 6–7 region. Sodium taurocholate effected a threefold reduction in the apparent K_m for α-l-fucosidase at pH 6.0, but studies on fucosidosis tissue (α-fucosidase deficiency) or subcellular fractions derived from rat liver failed to indicate the existence of a membrane-bound α-l-fucosidase. The response of other lysosomal hydrolases to the presence of bile salts was investigated and was found to be variable, perhaps depending upon the hydrophilic or hydrophobic nature of the natural substrate and/or the state of association of the active enzyme.     

Substrate specificity of ascorbate oxidase.

Ascorbate oxidase oxidizes leuco 2, 6-dichloroindophenol to the blue quinoid dye and produces spectral changes in the UV spectra of certain substituted polyhydric and amino phenols at pH 5.7. The new peaks produced by the addition of enzyme to the dichlorohydroquinones (2,5 and 2,6) and hydroxyhydroquinone correspond to the respective p-quinones of these substrates. At pH 5.7, the enzyme does not oxidize hydroquinone, barely oxidizes chlorohydroquinone, but oxidizes 2,6- and 2,5-dichlorohydroquinone and hydroxyhydroquinone at a rate about $\text{1}\text{12}$ that of ascorbic acid, with the uptake of one gram atom of oxygen per mole of substrate. A correlation has been found between the concentration of anion present in solution at pH 5.7 and the rate of oxidation of compounds of the hydroquinone series by the enzyme. The results indicate that an anionic form of the substrate is an important requirement of the enzyme specificity.     

Substrate specificity of vetebrate collagenase.

Substrate specificity of purified tadpole collagenase (EC 3.4.24.3) has been studied using eleven synthetic peptides. A pentapeptide, t-butyloxycarbonylprolylalanylglycylisoleucylalanine amide, was susceptible to the action of the enzyme and an octapeptide, acetylprolylglutaminylglycylisoleucylalanylglycylglutaminylarginine ethyl ester, was proposed to be the best substrate for vertebrate collagenase among the peptides tested.     

Immunochemical characterization of the adenine nucleotide translocator. Organ specificity and conformation specificity

Antibodies have been prepared against purified preparations of the heart and kidney nucleotide translocator in the 'c'-conformation. The results show organ-specific antigenic determinants on the translocator proteins isolated from heart, kidney and liver although a partial cross-reactivity between these three proteins was demonstrable. The organ specificity was observed both with the solubilized and with the membrane-bound translocator protein indicating organ-specific determinants on exposed regions of the carrier. An organ-specific inhibition of the nucleotide transport in heart mitochondria by the heart carboxyatractylate-protein antiserum leads to the conclusion that the organ specificity is at least partially conditioned by the binding site for the substrate and/or the closely linked gate of the carrier protein. Apart from the organ specificity the results also demonstrate a specificity of the antibodies for the translocational conformations of the carrier: the 'c'-conformation stabilized in the carboxyatractylate-protein complex and the 'm'-conformation present in the bongkrekate-protein complex. However, after denaturation of the carboxytraktylate-protein and bongkrekate-protein complexes the binding of the anti-(carboxyatractylate-protein) antiserum to both inhibitor-protein complexes was nearly identical. The conformation specificity was also expressed by the inhibition of the conformation transition from the 'c'- to the 'm'- state. This side-specific inhibition of the nucleotide transport and the identical binding activity of the carboxyatractylate-protein antiserum against the denatured carboxyatractylate-protein and bongkrekate-protein complexes suggested that the conformation-specific antigenic determinants are topographic surface regions which are determined by the chain folding.     

Cellular specificity of plasmacytoma-induced immunosuppression.

The pattern of immunodeficiency in plasmacytoma-bearing mice appears to be unique. Mice bearing these tumors exhibit a severe impairment in their ability to mount a primary immune response to thymus-dependent and -independent antigens. However, cell-mediated immune functions in these mice apparently remain intact. Thus, when T cell activity of lymph node cells from plasmacytoma-bearing mice was tested in vivo by sensitization with dinitrofluorobenzene and in vitro by responsiveness to phytohemmagglutinin, allogeneic cells, and dinitrobenzene sulfonate, cell-mediated immunity was found to be normal.     

Structural aspects of thrombin specificity.

Computer-assisted comparisons were made of the X-ray coordinates of all homologous atoms in the serine protease derivatives tosyl chymotrypsin Aα, tosyl elastase, and diisopropylphosphoryl trypsin. The results provided further quantitative support for the belief that sequence homology in proteins results in close similarity of conformation. On this basis, inferences were drawn about the three-dimensional structure of the serine protease thrombin, for which atomic coordinates have not yet been determined experimentally. Further, it was concluded that the unique specificity of thrombin, i.e., its selective cleavage of certain ArgGly bonds in fibrinogen, is unlikely to be due to the insertions in the amino acid sequence of thrombin or to differences in sequence in the region of the active site and binding pocket. It is possible, however, that the elongated A chain appended to thrombin may be a source of this specificity.