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Biomedical subjects

S G Cohen

Publications and source records attributed to S G Cohen.

At least 19 recordsLinked to original sources
PubMed1994

Active-site peptides of acetylcholinesterase of Electrophorus electricus: labelling of His-440 by 1-bromo-[2-14C]pinacolone and Ser-200 by tritiated diisopropyl fluorophosphate.

To characterize the structure of the active site of acetylcholinesterase (AChE) from the electric organ of E. electricus, we identified sites of incorporation of two active-site affinity labels, [3H]diisopropyl fluorophosphate ([3H]DFP), and 1-bromo-2-[14C]pinacolone ([14C]BrPin). AChE was isolated, purified, inactivated and digested with trypsin, and peptides containing 3H or 14C were purified by reverse-phase HPLC and characterized by N-terminal sequence analysis. [3H]DFP, labelling Ser-200, was found in a single peptide, QVTIFGESAGAASVGMHLLSPDSR, 83% identical with the sequence from Thr-193 to Arg-216 deduced for AChE of T. californica, with Gln, Ala, Leu, and Asp in place of Thr-193, Gly-203, Ile-210 and Gly-214, respectively, and 87% identical with that from bovine and human brain AChEs. Inactivation by [14C]BrPin led to two radioactive peptides. One, ASNLVWPEWMGVIHGYEIEFVFGLPLEK, was 96% identical with that extending from Ala-427 to Lys-454 of T. californica. Release of 14C in cycle 14 established reaction of [14C]BrPin with active-site His-440, protected by 5-trimethylammonio-2-pentanone (TAP). The other peptide, LLXVTENIDDAER, 77% homologous with that of T. californica extending from Leu-531 to Arg-543, had label associated with the third cycle, not protected by TAP, corresponding to Asn-533. The slow inactivation of eel AChE by reaction of [14C]BrPin at His-440 contrasts with that of AChE from T. nobiliana, where it reacts rapidly with a free cysteine, Cys-231, not present in eel AChE. For both AChEs, inactivation by BrPin prevents subsequent reaction with [3H]DFP, and prior inactivation by DFP does not prevent reactions with [14C]BrPin.

Acetylcholinesterase↗
PubMed1994

The use of magnetic resonance imaging to determine splint position in the management of internal derangements of the temporomandibular joint.

Internal derangements of the temporomandibular joint (TMJ) can elicit symptoms of pain, clicking and noises described subjectively as popping, grinding or grating. These symptoms may be the precursor of a more severe disease process such as degenerative joint disease (DJD) or osteoarthritis. The most common factor predisposing to degenerative changes within the TMJ is a displaced meniscus. Maintenance of a proper anatomic meniscal-condylar relationship is essential in preventing DJD. In the past, non-surgical treatment utilizing intraoral orthotic devices has been attempted to "recapture" the meniscus. The position of the meniscus was then evaluated merely by clinical examination due to the lack of modalities available to verify the meniscal position. The advent of magnetic resonance imaging (MRI) has changed this scenario. The meniscal position can now be visualized, thus enabling the practitioner to treat patients more effectively. Three case reports are presented in this study demonstrating the use of splint therapy utilizing MRI to determine meniscal position.

Adult↗
PubMed1993

Labeling of cysteine 231 in acetylcholinesterase from Torpedo nobiliana by the active-site directed reagent, 1-bromo-2-[14C] pinacolone. Effects of 2,2'-dipyridyl disulfide and other sulfhydryl reagents.

Acetylcholinesterase (AcChE, EC 3.1.1.7) was isolated from the electric organ of T. nobiliana and treated with the active-site-directed alkylating agent 1-bromo-2-[14C]pinacolone ([14C]BrPin), or with BrPin, which acts initially as a competitive inhibitor, Ki = 0.18 mM, and then inactivates the enzyme, k2 = 1.8 x 10(-4) s-1. AcChE aliquots were digested with trypsin and fractionated by reversed phase high performance liquid chromatography. Inactivation caused a decrease in one absorption peak and an increase in another, identified as the peptide beginning at Ala-222 and extending to Arg-242. 5-Trimethylammonio-2-pentanone, a competitive inhibitor, isosteric with acetylcholine, retarded the inactivation and decreased the quantity of labeled peptide. On sequencing, the 14C label was found associated with Cys-231. This was confirmed by comparison with synthesized S-pinacolonylcysteine, by study of effects of blocking the sequencing by o-phthalaldehyde, and by inactivation by 2,2'-dipyridyl disulfide (2-PDS), a thiol-specific reagent that acts initially as a competitive inhibitor, Ki = 0.042 mM, and then inactivates the enzyme, k2 = 5.0 x 10(-4) s-1. This is retarded by 5-trimethylammonio-2-pentanone, and prior inactivation by 2-PDS prevents subsequent reaction of [14C]BrPin in the active site. BrPin inactivates AcChEs from Electrophorus electricus and from human erythrocyte, but 2-PDS does not. Neither reagent inactivates butyrylcholinesterases from human and horse serum.

2,2'-Dipyridyl↗
PubMed1993

Intracranial schwannoma as atypical facial pain. Case report.

Facial pain is a common complaint that leads those who have it to seek professional help. Often times, the general dentist is the first clinician that a patient consults because of a presumed odontogenic origin of the pain. Occasionally a small number of these patients will be found to have an intracranial tumor. The case reported here is one such patient who was diagnosed and treated for a seventh nerve schwannoma.

Adult↗
PubMed1991

The hydrophobic photoreagent 3-(trifluoromethyl)-3-m-([125I] iodophenyl) diazirine is a novel noncompetitive antagonist of the nicotinic acetylcholine receptor.

We have shown previously that the lipophilic photoreagent 3-(trifluoromethyl)3-m-([125I]iodophenyl)-diazirine ([125I]TID) photolabels all four subunits of the Torpedo nicotinic acetylcholine receptor (AChR) and that greater than 70% of this photoincorporation is inhibited by cholinergic agonists and some noncompetitive antagonists, including histrionicotoxin (HTX), but not phencyclidine (PCP; White, B.H., and Cohen, J.B. (1988) Biochemistry 27, 8741-8751). We have now examined the effects of nonradioactive TID on (a) AChR photoincorporation of [125I]TID, (b) AChR-mediated ion transport, and (c) AChR binding of several cholinergic ligands. We find that TID inhibits [125I]TID photoincorporation into the AChR to the same extent as carbamylcholine. The saturable component of [125I]TID photolabeling is half-maximal at 4 microM [125I]TID with 0.5 mol specifically incorporated per mol of AChR after 30 min photolysis with 60 microM [125I]TID. Repeated labeling of membranes at a fixed [125I]TID concentration gave results consistent with a maximal incorporation of one [125I]TID molecule per AChR. Nonradioactive TID also noncompetitively inhibits agonist-stimulated 22Na+ efflux from Torpedo vesicles with an IC50 of 1 microM. Furthermore, TID inhibits allosterically the binding of [3H]HTX, decreasing its affinity for the AChR 5-fold both in the presence and absence of agonist. In contrast, TID has little effect on [3H]PCP binding in the absence of agonist but completely inhibits it in the presence of agonist. TID enhances the cooperativity of [3H]nicotine binding. [125I]TID is thus a photoaffinity label for a novel noncompetitive antagonist binding site on the AChR that is linked allosterically to the binding sites of both agonists and other noncompetitive antagonists. The [125I]TID site is presumably located within the central pore of the AChR.

Affinity Labels↗
PubMed1991

The differentiation of intraoral ulcers.

Oral lesions commonly seen by primary care physicians represent manifestations of local or systemic disease of infectious, immunogenic, malignant, or traumatic etiology. The patient's history will readily show whether the lesions are acute or chronic, single or multiple, primary or recurrent--classifications that greatly simplify the differential diagnosis.

Acute Disease↗
PubMed1991

General occurrence of binding to acetylcholinesterase-substrate complex in noncompetitive inhibition and in inhibition by substrate.

To assess the relative importance of binding to enzyme-substrate complex (E.S) and to acetylenzyme (EA), noncompetitive inhibition has been studied in hydrolysis by acetylcholinesterase (AcChE) of cationic and uncharged substrates - acetylcholine (AcCh), 3,3-dimethylbutyl acetate, n-butyl acetate, 2-(methylammonio)ethyl acetate, 2- (N,N-diethyl-N-n-butylammonio)ethyl acetate (DEBAAc) and 2-(methylsulfonyl)ethyl acetate. For the N-trimethyl quaternary ions related to AcCh, tetramethylammonium ion, choline and choline ethyl ether, noncompetitive inhibition (Ki(nonc) is more favorable with the slower substrates than with AcCh, i.e., when E.S greater than EA, and is attributed to formation of enzyme-substrate-inhibitor complexes, E.S.I'. Noncompetitive inhibition by tetraethyl-, tert-butyl- and isopropylammonium ions, and acetamidocholine and its lower dimethyl analogue, is also attributed to E.S.I' complexes. Peripheral binding of these inhibitors decreases acylation more than deacylation. Some tertiary dimethylamonio ions have more favorable Ki(nonc) values with AcCh, decreasing deacylation more than acylation. The substrate DEBAAc is a more effective noncompetitive than competitive inhibitor in hydrolysis of AcCh, indicating that it binds more strongly in a peripheral site than in the active site of the free enzyme. In its hydrolysis by AcChE, it acts as its own noncompetitive inhibitor, by this non-productive binding. Formation of E.S.I' complexes is a general characteristic of hydrolysis by AcChE and decrease in rates at high concentrations of AcCh and related substrates is attributed to peripheral regulatory site binding, formation of E.S.S' complexes, rather than to binding to the acetylenzyme.

Acetates↗
PubMed1989

Reactions of 1-bromo-2-[14C]pinacolone with acetylcholinesterase from Torpedo nobiliana. Effects of 5-trimethylammonio-2-pentanone and diisopropyl fluorophosphate.

1-Bromo-2-[14C]pinacolone, (CH3)3C14COCH2Br [( 14C]BrPin), was prepared from [1-14C]acetyl chloride and tert-butylmagnesium chloride with cuprous chloride catalyst, followed by bromination. It was examined as an active-site directed label for acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) (AcChE). AcChE, isolated from Torpedo nobiliana, has k(cat) = (4.00 +/- 0.04).10(3) s-1, Km = 0.055 +/- 0.008 mM in hydrolysis of acetylthiocholine, and k(cat) = (5.6 +/- 0.2).10(3) s-1, Km = 0.051 +/- 0.003 mM in hydrolysis of acetylcholine. BrPin, binding in the trimethyl cavity, acts initially as a reversible competitive inhibitor, Ki = 0.20 +/- 0.09 mM, and, with time, as an irreversible covalently bound inactivator. Introduction of 14C from [14C]BrPin into Torpedo AcChE at pH 7.0 was followed by SDS-PAGE, autoradiography and scintillation counting, in the absence and presence of 5-trimethylammonio-2-pentanone (TAP), a competitive inhibitor (Ki = 0.075 +/- 0.001 mM) isosteric with acetylcholine; 1.8-1.9 14C was incorporated per inactivated enzyme unit at 50% inactivation. TAP retarded inactivation by [14C]BrPin, and prevented introduction of 0.9-1.1 14C per unit of enzyme protected. Prior inactivation of AcChE by BrPin prevents reaction with [3H]diisopropyl fluorophosphate [( 3H]DFP). Prior inactivation by DFP or [3H]DFP does not prevent reaction with [14C]BrPin, and this subsequent reaction with BrPin does not displace the [3H] moiety. [14C]BrPin alkylates a nucleophile in the active site, and this reaction does not alkylate or utilize the serine-hydroxyl.

Acetylcholine↗
PubMed1988

Facial trismus and myofascial pain associated with infections and malignant disease. Report of five cases.

Five cases of facial pain and limited jaw opening, which include two infections, two primary carcinomas, and one metastatic carcinoma, each imitating TMJ dysfunction, are presented. These cases emphasize the importance of (1) a thorough working knowledge of the differential diagnosis of facial pain and limited jaw opening; (2) a complete evaluation, including a review of an adequate medical history as well as a full head and neck examination; and (3) the ability to make use of diagnostic radiographs, including computerized tomography.

Abscess↗
PubMed1987

Oral manifestations of disseminated Cryptococcus neoformans in a patient with acquired immunodeficiency syndrome.

A palatal lesion was the initial manifestation of disseminated cryptococcosis in a patient with acquired immunodeficiency syndrome (AIDS). The diagnosis was initially verified with cytologic smears in situ and later confirmed with pathologic findings from an excisional biopsy specimen. As cryptococcosis is one of the major opportunistic infections in persons with AIDS, an increased incidence of oral manifestations of cryptococcosis can be expected.

Acquired Immunodeficiency Syndrome↗
PubMed1987

A comparative study of herpes simplex infections in renal transplant and leukemic patients.

Herpes simplex virus (HSV) reactivation and lesion formation were studied in 68 renal transplant recipients and 30 leukemic patients. Antibody titers to HSV were determined, and seropositive patients were examined three times weekly for up to one month. Surveillance cultures were taken for oral HSV, and HSV culture and cytology were done for all oral lesions found. In a smaller number of patients, immune responses were determined. HSV reactivation was similar in the transplant and leukemic groups (46.8% vs. 50%), but a significant difference in the incidence of HSV lesion formation was noted between the two groups. Of the transplant patients in whom HSV reactivated, 31.8% developed HSV lesions; of leukemic patients in whom HSV reactivated, 100% developed HSV lesions. Differences in the incidence of formation of HSV lesions in these groups of immunosuppressed patients suggest that reactivation of HSV and formation of HSV lesions may involve different mechanisms. Low levels of antibody-dependent cellular cytotoxicity were noted in leukemic patients and may contribute to increased formation of HSV lesions in this group.

Adolescent↗
PubMed1987

Oral herpes simplex infections in patients with leukemia.

Thirty patients hospitalized for induction chemotherapy of acute leukemia were studied for incidence, severity, and clinical features of oral herpes simplex virus infections. In 50% of the patients with evidence of past herpes infection, recurrent oral herpes developed during the study. Herpes simplex virus was the major cause of oral mucosal lesions seen in patients with leukemia. A majority of the episodes involved multiple oral sites and caused large atypical lesions. All lesions healed after topical or intravenous acyclovir therapy. Herpes simplex infection should be ruled out in all cases of oral ulcers detected in patients being treated for leukemia.

Acute Disease↗