Biomedical subjects

R Guenther

Publications and source records attributed to R Guenther.

23 records · Page 2Linked to original sources

PubMed1993

5-Methylcytidine is required for cooperative binding of Mg2+ and a conformational transition at the anticodon stem-loop of yeast phenylalanine tRNA.

The role of modified nucleosides in tRNA structure and ion binding has been investigated with chemically synthesized RNAs corresponding to the yeast tRNA(Phe) anticodon stem and loop (tRNA(ACPhe). Incorporation of d(m5C) at position 14 of the stem of tRNA(ACPhe)-d(m5C14), CCAGACUGAAGAU-d(m5C14)-UGG, analogous to m5C40 in native tRNA(Phe), introduced a strong Mg2+ binding at a site distant from the m5C. A Mg(2+)-induced structural transition, detected by circular dichroism spectroscopy, was similar to that observed for the DNA analog of tRNA(ACPhe) (Guenther et al., 1992; Dao et al., 1992). In contrast, Mg2+ had little effect on unmodified tRNA(ACPhe)-rC14 or tRNA(ACPhe)-d(C14). Modified tRNA(ACPhe)-d(m5C14) bound two Mg2+ ions, and the binding was cooperative. The dissociation constant of the two Mg2+ ions from tRNA(ACPhe)-d(m5C14), 2.5 x 10(-9) M2, is the result of an RNA structure significantly stabilized by Mg2+ binding, delta G = -11.7 kcal/mol. The tRNA(ACPhe)-d(m5C14) structure, investigated by 1H NMR, had a double stranded stem of five base pairs and two additional base pairs across what was a seven membered loop in the unmodified tRNA(Phe)AC. Methylation of cytidine in the yeast tRNA(ACPhe) enables the molecule to form more than one conformation through a process regulated by Mg2+ concentration. Thus, the simplest of posttranscriptional modifications of tRNA, a methylation, is involved in a somewhat distant, internal-site Mg2+ binding and stabilization of tRNA structure, especially that of the anticodon stem and loop.

Anticodon↗

PubMed1983

Computerized tomography of a mediastinal pancreatic pseudocyst.

A pancreatic pseudocyst with mediastinal extension is demonstrated by ultrasound and CT. The value of these examinations compared to conventional radiography is stressed in establishing the correct diagnosis including differential diagnostic considerations.

Adult↗

PubMed1982

The serology of Sda effects of transfusion and pregnancy.

Pre- and posttransfusion antibody titers were performed on 6 patients with anti-Sda transfused with incompatible blood. In 3 of these patients a significant rise in IgG antibody titer was found. The data suggest that in occasional patients the Sda antigen does evoke a secondary immune response. We evaluated 245 pregnant women for the presence of Sda and found that 30% were Sd(a-). This incidence was significantly higher than that found in normal blood donors (4%), but was lower than that described in previous reports. We found that 22% of pregnant women in their first trimester were Sd(a-) whereas at term 36% were Sd(a-). These significantly different incidences of antigen positivity suggest decreased antigen expression with progressing pregnancy, as seen in the Lewis system. No difference was found in the incidence of anti-Sda between pregnant women, either during their first trimester or at term, and normal donors.

Blood Group Antigens↗

PubMed1978

Simultaneous balloon occlusion of the renal artery and hypothermic perfusion in in situ surgery of the kidney.

Renal ischemia and cooling may be achieved by intraluminal balloon occlusion and intermittent hypothermic perfusion using a double lumen, balloon-tipped catheter introduced into the renal artery percutaneously. This technique was used successfully in 26 of 31 extensive nephrolithotomies, eliminating the need for dissection and clamping of the renal artery and intricate surface cooling. Intrarenal operations could be performed as effectively as with clamp occlusion. Despite a mean ischemia time of 54 minutes the individual 131I-hippuran clearance of the operated kidneys was only reduced to a mean 78.4 per cent of the preoperative value 2 to 3 weeks postoperatively and increased to 92.2 per cent after 3 to 6 months, with a tendency toward further improvement.

Adolescent↗

PubMedDate not supplied

Effects of lithotripsy on rat kidney: evaluation with MR imaging, histology, and electron microscopy.

Magnetic resonance (MR) imaging at 1.5 T was used to evaluate the effects of extracorporeal shock wave lithotripsy (ESWL) in 30 rats and the findings on T1- and T2-weighted (spin echo 600/22, 1,600-2,000/90) images were compared with histology and scanning microscopy. The observed pathologic changes increased in severity with the number of shock waves given (500-5,000 15 kV). Post-ESWL MR findings in 54 kidneys included perirenal and subcapsular fluid (n = 30), diffuse loss of corticomedullary junction definition (n = 28), intrarenal foci of increased (n = 7) or decreased (n = 6) signal intensity, focal indentation of the renal contour (n = 5), and loss of distinction between the renal, splenic, or hepatic contour (n = 7). The subcapsular and intrarenal findings corresponded pathologically to areas of hemorrhage and hematoma formation--the contour changes to foci of renal scarring or perirenal adhesions. Electron microscopy demonstrated marked alterations of the renal tubules and vasculature. The study shows the feasibility of assessing the nature and chronology of renal damage post-ESWL in a rat model by MR.

Animals↗