Biomedical subjects

Y T Chu

Publications and source records attributed to Y T Chu.

3 recordsLinked to original sources

PubMed2001

N-glycosylation and residues Asn805 and Asn890 are involved in the functional properties of type VI adenylyl cyclase.

In this study, we demonstrate that type VI adenylyl cyclase (ACVI) is glycosylated in vivo. Treating HEK293 cells expressing ACVI with tunicamycin to block the addition of N-linked oligosaccharide or removing the N-linked oligosaccharide by in vitro peptidyl-N-glycosidase F digestion reduced the molecular mass of ACVI. Furthermore, tunicamycin treatment suppressed the forskolin-stimulated activity of ACVI. Mutation of either one or both potential N-glycosylation sites (Asn(805) and Asn(890), located on extracellular loops 5 and 6, respectively) also reduced the molecular mass of ACVI. Therefore, ACVI was glycosylated at both Asn(805) and Asn(890). Confocal analysis indicated that glycosylation was not required for the delivery of ACVI to the cell surface. Although no significant alterations in K(m) values for ATP or sensitivity to divalent cations were detected, the glycosylation-deficient ACVI mutant N805Q/N890Q-ACVI exhibited much lower forskolin-, Mn(2+)-, and Mg(2+)-stimulated cyclase activities than did wild-type ACVI. By contrast, the Galpha(s)-stimulated cyclase activities of wild-type ACVI and N805Q/N890Q-ACVI were indistinguishable. Furthermore, compared with wild-type ACVI, N805Q/N890Q-ACVI was less sensitive to inhibition mediated by dopamine D2 receptors or by protein kinase C. Collectively, glycosylation of ACVI not only affected its catalytic activity in an activator-dependent manner, but also altered its ability to be regulated by a Galpha(i) protein-coupled receptor or by protein kinase C.

Adenylyl Cyclases↗

PubMed2001

Pulmonary valvular stenosis complicated by cerebrovascular accident and congestive heart failure in a young child.

Pulmonary valvular stenosis (PS) with intact ventricular septum is a common congenital heart disease. In general, mild PS has a benign clinical course. However, in severe PS and some cases of moderate stenosis, increasing severity of the lesion may occur. The manifestations of either cerebrovascular accident (CVA) or congestive heart failure (CHF) are rarely reported in pediatric patients with PS. In this report, we describe a girl with severe PS complicated by seizures and sudden onset of hemiparesis at 13 months of age who developed CHF when 16 months old. CHF was cured after successful balloon valvuloplasty. She remained well without residual hemiparesis or recurrent seizures during the 1-year follow-up. Early balloon valvuloplasty should be emphasized in patients with severe PS, even if there are no significant clinical symptoms. With prompt balloon valvuloplasty, these complications can be effectively prevented.

Female↗

PubMed1992

Electrode-electrolyte interface impedance: experiments and model.

The impedance of the junction between a solid or aqueous electrolyte and a metal electrode at which no charge transfer processes occur (blocking contacts) follows closely the constant phase angle form, Z = A(j omega)-n, over a wide frequency range, where A is a constant, and the frequency exponent n is typically in the range of 0.7 to 0.95. Several models have been proposed in which the magnitude of the frequency exponent n is related by a simple expression to the fractal dimension d of the rough electrode surface. But experiments with aqueous H2SO4 and roughened platinum and silicon electrodes show that there is no simple relationship, if any at all, between n and d when d is determined from the analysis of one dimensional surface profiles. Moreover, n is not a simple function of the average roughness of the electrode. In order to gain some insight into the effect of electrode topography and the interface impedance, a model for the response of the interface to a constant voltage pulse was constructed. This model is based on the idea that, following a pulse, locally concentrated regions of ions accumulate rapidly at the tips of large protrusions on the electrode surface which screens deeper regions of the electrode from the field driven flux of mobile ions. After this rapid charging, ions are able to reach the deeper, screened regions of the electrode by diffusion, and it is this diffusive process that gives rise to the observed t1-n dependence of the charge collected. Computer simulations, similar to the diffusion limited aggregation model, using measured profiles as fixed (non-growing) clusters, gave exponents n in good agreement with experiment.

Computer Simulation↗