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Biomedical subjects

G Stevens

Publications and source records attributed to G Stevens.

101 records · Page 6Linked to original sources
PubMed1983

Reduction of laccase type 1 copper by 3,4-dihydroxyphenylalanine and other catechol derivatives.

3,4-Dihydroxyphenylalanine (DOPA) is not a preferred substrate of Rhus vernicifera laccase, as rate constants for the anaerobic reduction of the type 1 cupric atom by L-DOPA (6.3 X 10(1) M-1 s-1), D-DOPA (2.6 X 10(1) M-1 s-1), and L-DOPA methyl ester (2.6 X 10(1) M-1 s-1) are considerably smaller than k1 (catechol) (7 X 10(2) M-1 s-1) and rate constants characteristic of numerous other nonphysiological organic substrates (25 degrees C, pH 7.0, I = 0.5 M). The reactions of DOPA derivatives with laccase are unique, however, in that a two-term rate law pertains: kobsd = k0 + k1[phenol]; k0(L-DOPA) = 7 X 10(-2) s-1. The reactivities of other catechol derivatives (pyrogallol, gallic acid, and methyl gallate) with laccase type 1 copper were also examined.

Catechols↗
PubMed1982

Anation of laccase type 2 copper by azide and thiocyanate ions.

A mechanistic study of the anation of type 2 Cu(II) in fully oxidized laccase by azide and thiocyanate ions (X-) is reported. The rate data support a mechanism involving rapid formation of an outer-sphere complex (laccase . X-) followed by rate-limiting dissociative interchange to give the inner-sphere complex (laccase-X-) product: (formula; see text) Rate parameters for the laccase-azide reaction are k'2 = 1.25 X 10(-1) s-1 and k'-2 = 1.50 X 10(-2) s-1; those for the laccase-thiocyanate reaction are k'2 = 2.0 X 10(-2) s-1 and k'-2 = 1.1 X 10(-2) s-1 (25 degrees C, pH 6.1 phosphate buffer, I = 0.5 M). Although the rate law for anation of type 2 Cu(II) by N3- in 2-(N-morpholino)ethanesulfonic acid (Mes) or acetate medium (kobsd = k3 + k4[N3-]) differs from that observed in phosphate buffer, the data may still be accounted for in terms of the above mechanism, with Kos[N3-] much less than 1 [in Mes, k3 = 2.2 X 10(-2) s-1 and k4 = 3.3 X 10(-1) M-1 s-1; in acetate, k3 = 2.1 X 10(-2) s-1 and k4 = 3.4 X 10(-1) M-1 s-1 (25 degrees C, pH 6.0, I = 0.25 M)]. The equilibrium and spectroscopic characteristics of the laccase type 2 Cu(II)-N3- complex are compared with those of low molecular weight copper(II)-azide species, and the factors responsible for the very low substitutional reactivity of the type 2 cupric ion are discussed.

Anions↗
PubMed1980

Bias in atrributions of positive and negative behavior in children by school psychologists, parents, and teachers.

24 parents, 24 school psychologists, and 27 elementary school teachers viewed films of three different children and rated them using a 20-item, 9-point Likert-type instrument. The hypothesis that perceived socio-economic status and ethnic identification would differentially affect the three rater groups' attributions of positive and negative behavior was tested and supported. Results indicated that the three groups of raters were markedly different in their ratings of these children and that the children were rated more positively or negatively as a function of their socio-economic status and ethnic identification rather than as a function of their observable behavior.

Child↗
PubMedDate not supplied

Failure of argon laser to halt cytomegalovirus retinitis.

This report describes the experience with Argon laser used in an attempt to slow the advance of CMV retinitis in two eyes of two patients with AIDS, who were not able to be treated with antiviral chemotherapy. The treatment was performed to create a retinal scar to attempt to slow cell-to-cell spread of the virus through retinal tissue. In both patients, treatment was not successful in preventing spread of the CMV infection. Foci of retinitis, beyond the treated areas, became apparent within 2 weeks of treatment. Autopsy histopathology confirmed the diagnosis of CMV retinitis in both patients and necrosis due to CMV retinitis was seen in laser treated retina, and on both sides of laser treated retina.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Retropharyngeal synovial sarcoma in an infant: report of a case and of its response to chemotherapy; review of the literature.

Synovial sarcoma of the retropharynx is an extremely rare neoplasm. To date, only 10 cases have been reported in patients less than 15 years old. Our 15-month-old patient is, to our knowledge, the youngest ever reported with a retropharyngeal synovial sarcoma in the world literature. In the past, treatment usually consisted of surgery followed by radiotherapy or adjuvant chemotherapy, or both. In the case reported here, combination chemotherapy (ifosfamide, vincristine, and actinomycin D), used as the initial treatment modality, induced a dramatic decrease of the synovial sarcoma.

Antineoplastic Combined Chemotherapy Protocols↗