Search PubMed⌕ Search

Biomedical subjects

J L Mitchell

Publications and source records attributed to J L Mitchell.

At least 91 records · Page 5Linked to original sources
PubMed1982

Amine-specificity of the inactivating ornithine decarboxylase modification in Physarum polycephalum.

The enzyme catalysing the polyamine-stimulated modification of Physarum ornithine decarboxylase in vivo was partially purified and its activity on purified ornithine decarboxylase was examined with respect to its specificity for various amines. Spermidine, spermine and several polyamine analogues strongly promoted this reaction in vitro (apparent Km in the 0.1--0.5 mM range), whereas putrescine (apparent Km 5.33 mM) and several related diamines were not nearly as effective. In agreement with this, sensitivity studies performed in vivo also suggested that cellular spermidine, and not putrescine, is critical in modulating ornithine decarboxylase activity by this post-translational control. Unlike putrescine, or other diamines, 1,3-diaminopropane demonstrated a functional similarity to the polyamines in stimulating this reaction. This study has demonstrated a method whereby non-physiological amines capable of depressing ornithine decarboxylase activity by this natural feedback mechanism can be readily identified for further evaluation of their potential use in the experimental and medical control of polyamine biosynthesis.

Amines↗
PubMed1981

Protein factor which induces conversion between Physarum ornithine decarboxylase forms in vitro.

The rapid activity modulation of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) in Physarum polycephalum is closely correlated with a reversible post-translational modification of this enzyme. A factor has now been isolated from homogenates of exponentially-grown microplasmodia which catalyzes the conversion of the active enzyme form, A, into its less active, B state. Partial purification of this A-B converting factor has been achieved using DEAE-Sephacel chromatography and Ultrogel AcA-34 gel filtration. It appears to be a heat labile, acidic protein with a molecular weight of about 35 000 which binds to large macromolecules in crude fractions isolated using low ionic strength buffers. The in vitro converting reaction requires the presence of spermidine or spermine (1 mM) while putrescine is much less effective, and inorganic cations are ineffective at levels up to 5 mM. Enzyme conversion is reduced in elevated ionic strengths and in the presence of polyamine chelators such as ATP, ADP or GTP (1.0 mM). Under current assay conditions the interaction between ornithine decarboxylase and this factor is stoichiometric, yet it is not reversed even by conditions which favor dissociation of protein-protein interactions. This is the first report of the isolation of a protein factor which is involved in the interconversion of ornithine decarboxylase between its alternate enzyme states.

Carboxy-Lyases↗
PubMed1979

Phototoxic polyacetylenes and their thiophene derivatives. (Effects on human skin).

Polyacetylenes and their thiophene derivatives were tested for their effects on human skin. Topically applied alpha-terthienyl evoked bi-phasic phototoxic dermatitis and the appearance of 'sunburn' cells in human epidermis. None of 11 polyacetylenes had the same effect although they mimicked alpha-terthienyl in their phototoxic effects on Candida albicans and certain pathogenic microorganisms. The UV-mediated antibiotic activity of the compounds and their apparent lack of phototoxicity towards the skin suggest a potential topical therapeutic role for them in yeast, fungal and bacterial infections and light-responsive dermatoses. Their topical sensitizing capacity, however, has not yet been studied.

Alkynes↗
PubMed1978

Control of ornithine decarboxylase activity in Physarum by polyamines.

The addition of putrescine, spermidine, or spermine, to cultures of Physarum polycephalum rapidly reduced the activity of ornithine decarboxylase, with maximal inhibition, 80-90%, occurring after 90 min. This response was not due to a decrease in enzyme molecules, but rather to the rapid conversion of the active enzyme to a stable, catalytically less active form. This response to exogenous polyamines was not accompanied by the appearance of a macromolecular inhibitor (antizyme) either free, or bound to the enzyme. Physiological levels of the polyamines were also found to inhibit this enzyme in vitro both competitively and non-competitively, and to promote complete yet reversible inactivation of this enzyme in the absence of reducing agents. The data suggest that the control of this enzyme by endogenous polyamine levels may be distinct from its response to exogenous polyamines.

Buffers↗
PubMed1977

Physical and kinetic distinction of two ornithine decarboxylase forms in Physarum.

Two forms of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) can be isolated from crude plasmodial homogenates of Physarum polycephalum. Both forms catalyze the stoichiometric production of putrescine and CO2 from ornithine, yet they are distinguished by (a) a large difference in their affinity for coenzyme (apparent Km values of 0.13 and 33 muM); (b) a differential stability to extended dialysis of crude homogenates at 4 degrees C; and (c) the tendency of the low affinity form to polymerize when suspended in low ionic strength borate and phosphate buffers. These forms appear to be alternate states of a basic catalytic subunit in that (a) they both demonstrate monomer and dimer molecular forms of 80 000 and 160 000 daltons, respectively, depending on the buffer content; (b) they coelute from DEAE-Cellulose ion-exchange columns; and (c) they vary in activity in approximately equivalent yet opposite directions in response to factors which alter this organism's growth or metabolism. These data suggest that ornithine decarboxylase activity may be modulated by the control of the transition of this enzyme between the active and the relatively less active form.

Carboxy-Lyases↗
PubMed1977

Cold sterilization of gutta-percha cones with formocresol vapors.

Cold sterilization of gutta-percha cones was accomplished by exposing them to formocresol vapors for 16 hours. The data obtained from this in vitro study indicate that gaseous sterilization with formocresol vapors is effective against a variety of gram-positive, gram-negative, and spore-forming microorganisms.

Bacteria↗
PubMed1975

Experiences and observations with the typing of Staphylococcus aureus phage 94.

During a 28-month period, 5,078 cultures from a variety of anatomical sites were received for staphylococcal phage typing. Of these, 503 (10%) were not suitable for the procedure requested. Of the 4,575 viable cultures, 1,030 (23%) of the microorganisms were nontypable at both the routine test dilution (RTD) and at 100 times RTD. Of the 3,545 typable organisms, 3,061 (86%) were lysed at RTD, whereas 484 (14%) were typed only at 100 times RTD. Observations pertaining to the typing efficacy of staphylococcal phage 94 indicate that 651 (18%) of the typable microorganisms were lysed only by phage 94 at RTD or at 100 times RTD. Without the addition of this new phage to the international basic set, the number of nontypable strains (1,030 or 23%) would have been 1,681 (39%). Data regarding the geographic distribution of Staphylococcus aureus phage 94 point to the occurrence of the host strain in 13 (68%) of 19 states and 18 (62%) of the 29 hospitals submitting specimens to this laboratory. The assumed origin and speculated mode of dissemination of this microorganism are discussed.

Aerospace Medicine↗
PubMedDate not supplied

Modifying a childbirth education curriculum for two specific populations. Inner-city adolescents and substance-using women.

An interdisciplinary care provider team conducted a nonexperimental, observational, descriptive study to determine a childbirth education curriculum that would meet the needs of pregnant adolescent and substance-using women who attend prenatal clinics at an urban, municipal hospital center. A childbirth education curriculum, originally taught to a clinic population in 1974, was used with the two special populations in 1993 for a 7-month period. Participants were encouraged to provide feedback about the curriculum for each class by offering suggestions for additions or deletions of content. Provider staff also evaluated the content for applicability today. At the end of the study period, the pregnant adolescent group had been most involved with the class exercises; members of the group provided feedback about content. They were consistently positive in evaluating the entire six-class curriculum and recommended some additional topics. The adolescents demonstrated sustained interest in breast-feeding. The substance-using women, on the other hand, expressed a preference for content that focused on labor and birth; they preferred to ask questions, individually and in the privacy of the examining room, and showed negligible interest in breast-feeding.

Adolescent↗
PubMedDate not supplied

Cross-cultural issues in the disclosure of cancer.

PURPOSE: To increase awareness of cultural differences in the disclosure of a cancer diagnosis or prognosis, the author reviews several surveys of patients and physicians from around the world. OVERVIEW: The Western medical community is increasingly emphasizing full truthful disclosure of cancer diagnoses or prognoses and respect for autonomy as necessary prerequisites to ethical practice. However, surveys of European, Japanese, Native American, and various ethnic American (including Korean, Chinese, Mexican, Hispanic, African, and European American) cancer patients and physicians reveal that many cultures consider complete and accurate disclosure of cancer undesirable. Cultural differences in the rates of disclosure of a cancer diagnosis or prognosis; the physician's use of euphemisms to give a true or false diagnosis; as well as considerations of how to disclose a cancer diagnosis are described. CLINICAL IMPLICATIONS: Developing an awareness about cross-cultural practices regarding cancer disclosure issues allows the clinician to become more sensitive to the expectations of culturally and individually diverse cancer patients. To this end, all healthcare professionals should be informed about how the patient would like to be informed of a diagnosis and how involved he or she would like family members to be. In addition, an awareness of the use of nonverbal communication in some cultures and the psychosocial impact of certain terms, such as "cancer," is essential. Often, phrases such as "malignant tumor" or "growth" are less inflammatory and are more readily accepted. In ascertaining a knowledge of various cultural preferences and developing a sensitivity to these preferences, clinicians are better able to provide effective care to individuals from a variety of cultural and individual backgrounds.

Attitude to Health↗