PubMed Health⌕ Search

Biomedical subjects

D B Roberts

Publications and source records attributed to D B Roberts.

53 records · Page 3Linked to original sources
PubMed1975

Drosophila chromatin: an immunological study.

Antibodies were prepared against chromatin, various chromosomal protein preparations and against cytoplasm from Drosophila larvae. These antibodies were used to study the distribution of antigens in chromatin and chromosomal protein preparations on double diffusion plates. Antisera from all of the mammals tested precipitated both chromatin and DNA on double diffusion plates run in water. This non-specific precipitation was removed by washing in 0.06M NaCL.

Animals↗
PubMed1974

The preparation and characterisation of chromatin from third instar larvae of Drosophila melanogaster.

A procedure is described for the isolation of large amounts of chromatin from Drosophila third instar larvae. This material is suitable for immunisation of rabbits, and preliminary analysis by immunodiffusion reveals little cross reaction between chromatin and cytoplasm antigens, using antisera prepared against them. In addition to these studies, results from an examination of the exchange of radioactively labelled cytoplasmic proteins with nuclei suggest that no more than 5% of the total chromatin protein is of cytoplasmic origin. Electrophoretic analysis indicates that of this 5%, 20% migrates as a single band, in the same position as f2b histone. The techniques of radioactively labelling larvae which were used, may be suitable for achieving specific activities of up to 100muC/mg larval protein. Contamination of the chromatin by yeast proteins from the larval food is no more than 10%. Of this 30% is represented by one electrophoretic band. Immunological analysis reveals little cross reaction with yeast extracts. Electrophoretic and amino acid analyses of the chromatin proteins confirm earlier reports concerning Drosophila histones.

Animals↗
PubMed1972

Characterization and comparison of mycobacterial antigens by two-dimensional immunoelectrophoresis.

Two-dimensional immunoelectrophoresis (2D-IEP), in which a complex of antigens is subjected to electrophoresis first through an agarose matrix in one direction and secondly through an antiserum-agarose matrix at right angles to the first direction, was evaluated as a tool for analysis of mycobacterial antigens. Cell extracts from four species of mycobacteria, Mycobacterium tuberculosis (four strains), M. bovis strain BCG, M. scrofulaceum, and M. phlei, were assayed by 2D-IEP with four anti-mycobacterial antisera. Besides displaying the precipitin curves in a more easily interpreted format than did conventional immunoelectrophoresis (IEP), 2D-IEP offered greater sensitivity in terms of numbers of precipitin curves when like reactions were compared with IEP patterns. As many as 60 immunoprecipitates were observed on 2D-IEP slides compared to 18 on comparable IEP plates. Technical reproducibility of patterns from run to run was excellent. Other parameters, such as the influence of using different batches of antigen on the pattern, are discussed. Each of the cell extract antigens gave a unique pattern of precipitin peaks which could be easily differentiated from the patterns given by the other mycobacterial cell extracts when reacted with any of the antisera in 2D-IEP. Since both the species and strains of mycobacteria could be easily and reproducibly differentiated solely on the basis of two-dimensional immunoelectrophoretic patterns obtained with any of the antisera employed in this study, it may be possible, by using IEP, to differentiate and identify all species and strains of mycobacteria with one standard, highly sensitive antiserum, rather than a battery of antisera.

Animals↗
PubMed1967

Immunochemical studies on glutamate dehydrogenase and on two mutant forms of the protein.

Studies on the active product of pepsin digestion of rabbit immunoglobulin G (IgG), F(ab')(2) produced from antiserum against Neurospora glutamate dehydrogenase, showed it to behave in the same way, in both antienzyme and precipitation experiments, as homologous IgG. It is proposed that the inhibition of glutamate dehydrogenase by this antibody preparation is by the same mechanism as proposed for IgG and F(ab), a change in the configuration of the catalytic site brought about by antibodies. Antibodies prepared against two mutant proteins behaved in antienzyme studies in the same way as antibodies prepared against the wild-type protein. It is thought therefore that the antigenic sites on the mutant proteins which initiate the production of neutralizing antibodies were not affected by the mutation which had changed the catalytic properties of the mutant proteins.

Animals↗
PubMed1966

Immunochemical and enzymatic studies and glutamate dehydrogenase and a related mutant protein from Neurospora crassa.

Roberts, D. B. (University of Cambridge, Cambridge, England). Immunochemical and enzymatic studies on glutamate dehydrogenase and a related mutant protein from Neurospora crassa. J. Bacteriol. 91:1888-1895. 1966.-When an investigation was made of the inhibition of Neurospora glutamate dehydrogenase by bivalent and univalent antibodies, it was shown that the enzyme inhibition is not complete even with excess antibodies. The residual activity was some three times greater with bivalent antibodies, in spite of the observation that the ratio of inhibiting antibodies to catalytic sites was 2:1 for both types of antibody. Substrates did not affect the inhibition of enzyme activity, nor did antibodies affect the K(m) for either substrate. An allosteric mechanism for the inhibition of glutamate dehydrogenase by antibodies is proposed. It was also demonstrated that the mutant protein am-3 can be activated, to show glutamate dehydrogenase activity, by a number of activators. The requirement for the activation was the presence of a carboxymethyl group. The data suggest that the nonactivated protein has two combining sites for l-glutamate: the catalytic and activating sites. The wild-type enzyme has only one of these sites. Because the activating site is distinct from the catalytic site, an allosteric mechanism was postulated for activation. Inhibition of am-3 activity by antibodies is achieved either by a mechanism similar to the inhibition of wild-type activity or by the antibodies preventing the activation of the mutant protein. The am-3 protein can be activated by antibodies. Consequently, there appeared to be a relation the phenomena of enzyme inhibition and am-3 activation by antibodies; i.e., they alter the configuration of the catalytic site. This alteration was necessary for the activation of am-3, but inhibited the activity of the wild-type enzyme.

Antibodies↗