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Biomedical subjects

M Cohn

Publications and source records attributed to M Cohn.

At least 199 records · Page 11Linked to original sources
PubMed1973

The use of bacterial lipopolysaccharides to show that two signals are required for the induction of antibody synthesis.

Evidence is presented that antigen-sensitive cells require two signals for induction. Normally these two signals are delivered to the cell via the recognition of two determinants on the immunogen: the first the receptor on the antigen-sensitive cell, and the second by the cooperating cell system. The special experimental situation described here depends upon the observation that bacterial lipopolysaccharides (LPS) render immunogenic a variety of haptens. When monovalent haptens (TNP-amino acids) are added to spleen cultures, specific antihapten responses are induced in the presence of LPS. After analyzing competing interpretations of this phenomenon, we propose that the antigenic signal is delivered as the consequence of a conformational change in the receptor upon interacting with antigen, and the second signal is delivered directly via the interaction of LPS with the membrane on the antigen-sensitive cell receiving the antigenic signal, or indirectly via the interaction of LPS with the cooperating cell population. These data imply LPS is not itself a mitogen, but merely completes an inductive stimulus to B cells. The experimental results from these and other studies indicate how these two signals may participate in inductive, suppressive, and paralytic stimuli to antigen-sensitive cells.

Animals↗
PubMed1973

Dependence of the proton magnetic resonance spectra on the oxidation state of flavodoxin from Clostridium MP and from Peptostreptococcus elsdenii.

The broadening of protein nuclear magnetic resonances in the spectra of the semiquinone forms of flavodoxins derived from Clostridium MP and Peptostreptococcus elsdenii relative to the resonances in the oxidized and reduced forms is highly selective. Spectra from both species of flavodoxin indicate that conformational differences between the oxidized and fully reduced states are minor and, consequently, the broadening in the semiquinone form is ascribed to the paramagnetic effect of the flavin free radical. The chemical shifts of the paramagnetically broadened lines are used in conjunction with x-ray crystallographic models to assign peaks to amino-acid residues in the proximity of the flavin mononucleotide. Species-dependent differences in the spectra can generally be attributed to differences in amino-acid composition and sequence. The spectra from both species of flavodoxin indicate that there is slow exchange between oxidized and semiquinone forms or reduced and semiquinone forms of the flavodoxins with a limit of k(ex) < 50 sec(-1) for the exchange rate.

Amino Acid Sequence↗