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Biomedical subjects

S B Smith

Publications and source records attributed to S B Smith.

At least 217 records · Page 12Linked to original sources
PubMed1981

Cyclic AMP-dependent protein kinase I: cyclic nucleotide binding, structural changes, and release of the catalytic subunits.

Type I cyclic AMP (cAMP)-dependent protein kinase is composed of a dimeric regulatory subunit (R(2)) and two catalytic subunits (C subunits). The R(2) dimer binds four cAMP molecules to release the two C subunits. To characterize the cAMP binding sites and elucidate their role in the release of the C subunits, the R(2) dimer has been studied by equilibrium methods. The cAMP titration of R(2) was monitored by endogenous tryptophan fluorescence, and the results suggest one class of binding sites. The titration plot is monotonic for saturation of four sites per R(2). A similar titration monitored by near-UV circular dichroic changes exhibited profound changes in the region of the (1)L(b) tyrosine and (1)L(a) and (1)L(b) tryptophan transitions; a plot of these data also showed a linear monotonic response. Thus, the fluorescence and circular dichroic changes show that cAMP binding to R(2) induces a conformational or structural change. The one apparent class of binding sites implies that all binding sites are characterized by similar K(d) values or by K(d) values much less than the receptor concentration. The reactivity of the cysteine sulfhydryl groups with 5,5'-dithiobis(2-nitrobenzoic acid) showed that saturation with cAMP indirectly protects one sulfhydryl group per R monomer. Analysis of cAMP activation of the holoenzyme, detected by phosphotransferase assays, showed that saturation of both cAMP binding sites per R monomer is necessary to effect the release of the C subunit. By using a fluorescent analog of cAMP, 1,N(6)-etheno-cyclic AMP (epsilon cAMP), the (epsilon cAMP)(4).R(2) complex was titrated with C subunit, causing the release of epsilon cAMP. The titration showed that the release of epsilon cAMP was a positive cooperative process; its Hill plot had a slope of 2.6 and the K(a1) and K(an) values obtained by extrapolation were 2.1 x 10(7) M(-1) and 5.0 x 10(8) M(-1), respectively. The calculated DeltaDeltaG for first and last site coupling was 1.9 kcal/mol (1 cal = 4.18 J) of holoenzyme.

Animals↗
PubMed1981

Regulation of pyruvate kinase by 6-phosphogluconate in isolated hepatocytes.

Isolated liver parenchymal cells from rats fed a 65% sucrose diet for 14 days were incubated in the presence and absence of 10(-6) M glucagon. The pyruvate kinase obtained from homogenates of the glucagon-treated cells displayed and increased Ks 0.5 for phosphoenolpyruvate (P-enolpyruvate), as well as an increased Ka 0.5 for 6-phosphogluconate (6-P-gluconate), compared to pyruvate kinase from untreated cells. Additionally, glucagon treatment decreased the maximal stimulation of pyruvate kinase by 6-P-gluconate by approximately two-thirds and decreased the Hill coefficient value of pyruvate kinase for 6-P-gluconate from 1.76 to 1.56. 6-Aminonicotinamide, an inhibitor of 6-P-gluconate dehydrogenase, increased 6-P-gluconate levels in isolated liver parenchymal cells three- to sevenfold, depending on the substrates present. The flux of P-enolpyruvate through pyruvate kinase was increased from 18 to 40% in these preparations and was highly correlated with the increase in 6-P-gluconate levels. The results suggest that 6-P-gluconate could regulate pyruvate kinase activity in the intact liver parenchymal cell. Furthermore, the activator would be of greatest importance in the lipogenic animal.

Animals↗
PubMed1981

Experience with subclavian vein for vascular access.

We report our experience with the subclavian vein as a route for temporary vascular access. By modifying the technique described by Uldall one can place these catheters at the bedside without the need of a separate exit tunnel. They are easily maintained in place and allow for early discharge home while awaiting permanent vascular access maturation. The results of approximately 600 dialysis treatments showed adequate clearence with a mean postdialysis drop in creatinine of 5.0mg./dl. and BUN of 46mg./dl. Complication rates were minimal with no hemo or pneumothorax. The rate of complications between bedside and operating room placement was not different. We feel the low complication rate, the ease of insertion, and the patency at home makes this an attractive alternative to other means of temporary dialysis such as: peritoneal dialysis, repeat femoral vein catheterization or arteriovenous shunts.

Catheterization↗
PubMed1981

Results of hemodialysis & hemoperfusion in the treatment of acute arsenic ingestion.

Hemodialysis and charcoal hemoperfusion have been used in the last few years for the treatment of acute toxin ingestion. We used these methods to treat a patient with a known ingestion of 1.3 grams of arsenic trioxide. We measured blood and urine levels of arsenic prior to and after dialytic therapy in addition to before and after conventional chelation therapy. The blood and urine levels showed no significant change with any therapy and clinically he lapsed into prolonged coma. In view of the lack of laboratory and clinical response, we feel that hemodialysis and hemoperfusion may not be indicated in acute massive ingestion. Supportive care to maintain blood pressure and urinary output may be all there is to offer. In recent years both hemodialysis and hemoperfusion have been introduced as treatment of accidental or deliberate drug or toxin ingestion. (1-4) There have been previous reports on the supposedly successful treatment of arsenic ingestion with hemodialysis. (5-6) We report our experience with a massive ingestion of arsenic trioxide. This patient received treatment with conventional chelating agents, standard hemodialysis, as well as hemoperfusion, without evidence of significant removal of arsenic or clinical benefit.

Adult↗
PubMed1981

Effects of naturally acquired mixed helminth parasitism in yearling dairy calves.

The effects of Strongyle parasitism were studied in yearling calves. One group (4 calves) was a noninfected control, and 2 groups (4 calves each) were infected by exposure on pasture to the same type and degree of parasitism. One of the 2 infected groups were given coumafos at 4-week intervals and the other was not treated. Few significant differences were found between the control and infected groups in hematologic and serum glucose and urea nitrogen values. The control group gained an average of 2.2 kg/week, as compared with 1.0 kg/week, as compared with 1.0 kg/week for the treated group. The parasitized-untreated group lost 0.2 kg/week. Overall, the control group gained 26.8 kg for the 12-week period, which was significantly different (P less than 0.05) from an 11.4-kg gain by the parasitized-treated group and a 2.3 kg loss for the parasitized-untreated group. In the face of constant pasture challenge exposure, most adult worms were eliminated from the drug-treated animals, but the adverse effects of parasitism were not reversed.

Animals↗
PubMed1980

The purification and characterization of delta 5-3-ketosteroid isomerase from Pseudomonas putida, a cysteine-containing isomerase.

A delta 5-3-ketosteroid isomerase (EC 5.3.3.1) has been isolated from Pseudomonas putida Biotype B and purified to homogeneity. This previously undescribed steroid isomerase resembles that isolated from Pseudomonas testosteroni (Talalay, P., and Wang, V.S. (1955) Biochim. Biophys. Acta 18, 300-301). The enzyme is induced by various steroids, has a subunit molecular weight of 13,750 +/- 250, a pI of 4.8 +/- 0.1 has a specific activity of 40,000 units/mg, using 5-androstene-3,17-dione as the substrate. The amino acid composition of the enzyme subunit is Lys 2, His 2, Arg 8, Asp 11, Thr 5, Ser 4, Glu 17, Pro 8, Gly 12, Ala 12, Val 10, Met 5, Ile 6, Leu 8, Tyr 4, Phe 4, and Cys 4. The amino acid sequence has been determined for the NH2-terminal 50 residues. This portion of the polypeptide chain is approximately 47% homologous with the amino acid sequence of the first 50 residues of the delta 5-3-ketosteroid isomerase from P. testosteroni. The amino acid sequence of residues 33 to 41 of the P. putida isomerase is identical with the region Ala 31 through Pro 39 in the P. testosteroni enzyme. Residue 40 of the P. putida enzyme is aspartic acid and corresponds in the sequence to Asp 38 of the P. testosteroni isomerase, which has been shown to be essential for enzymatic activity (Ogez, J.R., Tivol, W.F., and Benisek, W.F. (1977) J. Biol. Chem. 252, 6151-6155).

Amino Acid Sequence↗
PubMed1980

Active site-directed photoinactivation of delta 5-3-ketosteroid isomerase from Pseudomonas putida dependent on 1,4,6-androstatrien-3-one-17 beta-ol.

delta 5-3-Ketosteroid isomerase from Pseudomonas putida is subject to photoinactivation by light of wavelengths greater than 300 nm, specifically in the presence of the competitive inhibitor, 1,4,6-androstatrien-3-one-17 beta-ol (TEO). In the absence of this steroid or in the presence of the nonchromophoric steroidal competitive inhibitor, deoxycholate, the enzyme activity is essentially unaffected by irradiation. Deoxycholate protects the enzyme from the TEO-dependent reaction to a degree which is predictable from the concentrations of deoxycholate and TEO and their respective competitive inhibition constants, thus demonstrating that the inititial velocity of the photoinactivation is dependent upon the fraction of enzyme active sites occupied by TEO. Cholate, which is not a competitive inhibitor, does not protect enzyme activity. Amino acid analyses of hydrochloric acid hydrolysates of the photoinactivated enzyme show no significant differences from that of the native enzyme. However, the fraction of initial enzyme activity remaining correlates quantitatively with the disappearance of one of the four thiol groups in each polypeptide chain of the enzyme. Enzyme irradiated under the same conditions in the absence of TEO does not lose thiol groups.

Amino Acids↗
PubMed1980

Papillary carcinoma of the thyroid, oxyphil cell type, "clear cell" variant: a light- and electron-microscopic study.

A unique case of papillary carcinoma of the thyroid having the combined features of three morphological subtypes--tall cell, clear cell and Hürthle cell--has been studied by light and electron microscopy. The distinctive neoplastic cells had an oxyphilic basal zone, a mid-placed nucleus and a clear apical region. Ultrastructurally, the cytoplasm was virtually filled with mitochondria, characteristic of Hürthle cells, but the unusual finding was the marked distention and emptiness of those mitochondria located in the apical zone, accounting for the clear phenomenon noted by light microscopy. In contrast, the mitochondria in the basal, or oxyphilic, part of the cells were intact. While a few cases of clear cell and papillary clear-cell carcinoma of the thyroid have been studied by electron microscopy previously, the clear change has never been attributed to dilated mitochondria, but rather to the presence of glycogen. The reason for the mitochondrial swelling is not answered, but it is probably an in vivo effect. Some of the other characteristics of papillary carcinoma of the thyroid described previously, such as microvilli, absence of colloid, infolded nuclei and nuclear bodies, were also present in this case. However, ground-glass nuclei, a frequently reported feature, were not found.

Carcinoma, Papillary↗
PubMed1977

Re-evaluation of amino-oxyacetate as an inhibitor.

Data are provided which indicate that pyruvate and/or acetaldehyde can reverse the inhibition of alanine aminotransferase and aspartate aminotransferase by amino-oxyacetate. It was shown that acetaldehyde could reverse the inhibition of gluconeogenesis from alanine and that pyruvate could reverse the inhibition of urea synthesis by amino-oxyacetate.

Acetaldehyde↗