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T Y Li

Publications and source records attributed to T Y Li.

32 records · Page 2Linked to original sources
PubMed1981

On the reactivity of metallothioneins with 5,5'-dithiobis-(2-nitrobenzoic acid).

Rat liver and horse kidney metallothioneins react with 5,5'-dithiobis-(2-nitrobenzoic acid) (Nbs2) to release 5-thio-2-nitrobenzoate and metal ions. The reactions are slow and exhibit biphasic kinetics with each process having an empirical rate law of the form: rate - k[RSM] X [Nbs2] + k'[RSM], where RSM represents mental-bound thiolate groups. The pseudo-first-order rates are insensitive to pH but are modified in guanidine hydrochloride solution. Rat liver metallothioneins of variable zinc, copper and cadmium composition react similarly and give observable thiol/total metal ratios in good agreement with stoichiometries of SH/(Cd + Zn) of 3 and SH/Cu of 1. A model complex cadmium-2,3-dimercaptopropanol, resembles the proteins in its reaction with Nbs2.

Animals↗
PubMed1980

Ligand substitution reactions of metallothioneins with EDTA and apo-carbonic anhydrase.

The reactions of Zn-, Zn,Cd-, and Cd-thioneins with EDTA and apo-carbonic anhydrase have been studied. The ligand substitution reaction of zinc with EDTA is multiphasic, having both associative and dissociative components in the rate expression. The cadmium sites are about 2 orders of magnitude less reactive. In contrast, apo-carbonic anhydrase abstracts zinc from Zn-thionein and Zn,Cd-thionein in second-order processes that are 2-3 orders of magnitude more rapid than those involving EDTA and approach the rate for unligated Zn2+ with the apo-protein. In comparison with other zinc proteins, Zn-thionein contains unusually reactive metal sites, suggesting that this protein may be a physiological zinc transfer protein, able to donate zinc to zinc-requiring apo macromolecules.

Animals↗
PubMed1979

Resonance Raman study of flavins and the flavoprotein fatty acyl coenzyme A dehydrogenase.

The resonance Raman (RR) spectra of FMN, FAD, FAD in D2O, and 7,8-dimethyl-1, 10-ethyleneisoalloxazinium perchlorate have been obtained by employing KI as a collisional fluorescence-quenching agent. The spectra are very similar to those obtained recently by using the CARS technique to eliminate fluorescence. Spectra have also been obtained for several species in which flavin is known to fluoresce only weakly. We report RR spectra of protonated FMN, FMN semiquinone cation, the general fatty acyl-CoA dehydrogenase, and two "charge-transfer" complexes of fatty acyl-CoA dehydrogenase. Tentative assignment of several vibrational bands can be made on the basis of our flavin spectra. RR spectra of fatty acyl-CoA and its complexes are consistent with the previous hypothesis that visible spectral shifts observed during formation of acetoacetyl-CoA and crotonyl-CoA complexes of fatty acyl-CoA dehydrogenase result from charge-transfer interactions in which the ground state is essentially nonbonding as opposed to interactions in which complete electron transfer occurs to form FAD semiquinone. The only significant change in the RR spectrum of FAD on binding to enzyme occurs in the 1250-cm-1 region of the spectrum, a region associated with delta N--H of N-3. The position of this band in fatty acyl-CoA dehydrogenase and the other flavoproteins studied to date is discussed in terms of hydrogen bonding between flavin and protein.

Acyl-CoA Dehydrogenases↗
PubMed1977

Determination of ionization state by resonance Raman spectroscopy Sulfonamide binding to carbonic anhydrase.

Resonance Raman (RR) spectroscopy has been used to study the ionization state of the sulfonamide, 4'-sulfamylphenyl-2-azo-7-acetamido-1-hydroxynaphthalene-3,-6-disulfonate (Neoprontosil), bound to carbonic anhydrase. The correlation of effects of pH and deuteration on the spectra of model compounds with these effects on the Neoprotosil spectrum allows us to assign spectral bands in the 900-1000 and 100-1200 cm-1 regions to the SO2NH2 group. Large shifts in these bands occur upon ionization of the sulfonamide. On the basis of the positions of bands in the enzyme complex, it was determined that the sulfonamide was bound to the enzyme as SO2NH2, rather than as SO2NH-. Rates of association and dissociation and the dissociation equilibrium constant were measured as a function of pH. The rate behavior for Neoprontosil is consistent with that observed for other sulfonamides and kdissoc/kassoc = kdissoc, suggesting a one-step binding mechanism. Since RR spectroscopy establishes that the final ionization state of the sulfonamide in the enzyme complex is SO2NH2, protonated sulfonamide must bind directly to basic form of the enzyme. These conclusions suggest that sulfonamides form "outer-space" complexes with metal at the enzyme active site.

Animals↗
PubMedDate not supplied

A partnership model of distance education: students' perceptions of connectedness and professionalization.

This article describes a partnership model of distance education for a master's nursing program in a midwestern state and an evaluation that assessed students' perceptions of professionalization and connectedness in the program. Students at the originating and distance sites were asked to complete evaluations at the end of each course. Connectedness and professionalization were measured using rated satisfaction with three modes of contact for each item. Results indicated that students at the distance site had a significantly higher overall level of satisfaction with interactive television (ITV) and experienced high levels of connectedness and professionalization through the ITV courses. However, among the three modes of connectedness, students at the distance site rated satisfaction with contact with same-site students as the highest, followed by contact with the instructor. Students also perceived that their professional identity increased through the three modes, particularly for contact with same-site peers at the distance site and for contact with instructors at both sites. Recommendations for faculty and student responsibilities are provided to ensure a positive learning environment.

Adult↗