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Biomedical subjects

C Cohen

Publications and source records attributed to C Cohen.

At least 487 records · Page 27Linked to original sources
PubMed1967

Allograft rejection in C'6 defective rabbits.

27 skin allografts were transplanted in duplicate to 13 rabbits defective in the sixth component (C'6) of complement (C'). 14 were rejected within the normal period of time and 9 only after a significant delay. In four grafts, no rejection was observed. Grafts exchanged between C' active and C' defective littermates tended to persist viable longer on the C' defective partners. It is concluded that in a species of higher vertebrates, the rabbit, allograft rejection can proceed in the absence of C'6 and the biological functions depending on it. This includes the cytotoxic function of complement. However, the prolonged survival in C'6 defective rabbits of some allografts strongly suggests that two pathways may be operative in the rejection reaction. The results are consistent with the view that a mechanism independent of C'6 was alone fully effective in the majority of the donor-host combinations. A C'6-dependent mechanism became influential only in some specific donor-host combinations.

Animals↗
PubMedDate not supplied

Nicotine dependence: a preventable risk factor for other diseases.

Nicotine meets all critical criteria for an addictive drug. Furthermore, there is no evidence that there would be widespread compulsive use of tobacco without nicotine. These findings have led to consideration of the cigarette as a contaminated vehicle for an addictive drug (nicotine). Nevertheless, nicotine itself may also be used therapeutically to reduce exposure to carcinogens and other tobacco toxins. Nicotine replacement is a useful adjunct in treating tobacco dependence. For example, nicotine replacement in the form of a polacrilex resin (chewing gum) can alleviate physically based signs and symptoms of tobacco abstinence. The fact that this form of nicotine replacement is not attractive to non-users of tobacco has opened the door to the use of nicotine in a therapeutic modality, permitting hope of eliminating tobacco dependence.

Chewing Gum↗
PubMedDate not supplied

A new myosin fragment: visualization of the regulatory domain.

Many of the functional domains of the myosin molecule have been defined by the use of proteolytic enzymes. Major fragments that retain enzymatic or assembly properties have been prepared by cleavage in the rod to form heavy meromyosin (HMM) and light meromyosin (LMM) or at the head-rod junction to form S-1 and rod. Limited tryptic digestion of vertebrate skeletal myosin S-1 indicates that the head contains three major regions: an amino-terminal nucleotide binding domain of molecular weight (MW) 25,000, a central domain of MW 50,000 and a carboxyl domain MW 20,000; the latter two are both able to bind to actin. Tryptic digestion of scallop S-1 has also been used to isolate a head fragment MW 14,000 associated with both types of scallop light chains. Here we report that myosin from vertebrate (chicken and rabbit skeletal) and molluscan (scallop adductor) striated muscles is cleaved in an unusual way with an enzyme from Pseudomonas aeruginosa. This bacterial protease (designated Ps-1) does not cleave myosin at the head-rod junction or in the rod; instead, Ps-1 splits the myosin heavy chain within the head, yielding a complete rod joined to the 20,000-MW head domains. The scallop regulatory and essential light chains remain associated with this fragment. We examined this new fragment by electron microscopy; the rods bear two 'nubs' about 100 A long, which appear to correspond morphologically to the neck region of the myosin molecule.

Animals↗
PubMedDate not supplied

Alpha-helical coiled-coil structures of Trypanosoma brucei variable surface glycoproteins.

We have used electron microscopy to examine purified intact variable surface glycoproteins (VSGs) from clones derived from two distinct stocks of Trypanosoma brucei. The VSG molecule from MITat 1.2 has a large elongated domain consistent with the shape of the dimeric N-terminal domain determined by X-ray analysis (see preceding paper), and a heretofore unseen short, thin fibrous tail presumed to be the C-terminal domain. Electron microscopy on DiTat 1.3, however, indicates a morphology quite distinct from that of MITat 1.2. Analysis of four VSG amino acid sequences reveals 7-fold periodicities (heptad repeats) which indicate that alpha-helical coiled-coil secondary structure elements occur in all of these VSGs, consistent with the observation of helical bundles in one VSG. These results suggest the possibility that VSG antigenic diversity may be related to a diversity in length and disposition of alpha-helical bundles and coiled-coil domains.

Animals↗