Health Indicators for Renal Replacement Therapy in Saudi Arabia

The renal replacement therapy in Saudi Arabia has 3 main modalities: hemodialysis, peritoneal dialysis, and renal transplantation. Hemodialysis is one of the fastest growing industries of health care providers in Saudi Arabia.

OBJECTIVE

We aimed to review the health indicators of renal replacement therapy.

MATERIALS AND METHODS

We used the Saudi Center for Organ Transplantation Annual Report 2016.

RESULTS

Patients with end-stage renal disease on hemodialysis and peritoneal dialysis totaled 17,687. Saudi Arabia increased the numbers of dialysis centers and also added 2 more sectors. The Ministry of Health hospitals have 55% of the centers, government non-Ministry of Health has 9%, private and charitable hospitals have 21%, the King Abdullah Hemodialysis Project has 2%, and the outsourcing dialysis programs have 13%. There are 243 dialysis units in Saudi Arabia. Most dialysis centers are in the central region (30%); 27% are in the western region, 19% are in the southern region, 13% are in the eastern region, and 11% are in the northern region. The average net increase of dialysis patients is 6.2% annually and is projected to reach 22,000 by 2020. Causes of renal failure are mainly diabetic nephropathy (40%) and hypertensive nephropathy (38%). Hepatitis C virus positivity is at 12% and hepatitis B surface antigen positivity is at 4%. From the year 2000 renal transplantation from deceased and living donation has tripled in number, with a total of 798 kidneys transplanted.

CONCLUSION

Renal replacement therapy is increasing and dialysis center numbers are expected to increase. Renal transplantation numbers have improved both from living and deceased donors but further actions toward the promotion of the organ donation in Saudi Arabia is essential.

Control for delayed bilateral teleoperation of a quadrotor

This paper proposes a cascade control scheme for delayed bilateral teleoperation of a quadcopter. The strategy transforms a 6D real quadcopter to an easy-to-teleoperate 3D virtual quadcopter. The scheme is formed by a P+d plus PID controller for each dof. The analysis based on Lyapunov theory gets as result the way to set the control parameters depending on the magnitude of the asymmetric time delays (forward and backward delays). This technic aims to reach stability, simplicity and good performance in practice. Besides, experimental tests about delayed bilateral teleoperation of a quadcopter including the proposed control scheme are shown in order to evaluate the system performance.

DETERMINACIÓN DE GÉNEROS BACTERIANOS EN EL MAR DE LA PLAYA CANTOLAO – LA PUNTA – CALLAO

Los océanos albergan una gran diversidad biológica, hasta el momento relativamente poco explorada por el humano. Con el objetivo de ampliar los conocimientos en la biodiversidad bacteriana del mar peruano, se realizaron muestreos aleatorios en el mar de Playa Cantolao-La Punta-Callao (12º04´06´´ S 77º10´10´´O), en total se tomaron 5 muestras en frascos estériles a una profundidad de 3 m utilizando una vara de madera acondicionada a una jeringa de 20 ml. Para el aislamiento se utilizó el método de dispersión en placa en Agar Marino, se trabajó con diluciones sucesivas para obtener colonias aisladas. Para la identificación se realizaron pruebas bioquímicas que incluían determinación de citocromo oxidasa, motilidad, producción de H2S, producción de indol, metabolismo de glucosa, producción de pigmento, luminiscencia, catalasa y desarrollo en anaerobiosis; además de las coloraciones Gram y de espora. Los esquemas propuestos por Das S et al. (2007), Oliver J (1982) y el Bergey´s Manual 2da y 7ma edición fueron utilizados para la determinación de géneros. Se logró el aislamiento de 20 cepas bacterianas. Los géneros encontrados fueron: Moraxella, Bacillus, Acinetobacter, Vibrio, Aeromonas, Photobacterium, Alteromonas, Alcaligenes, Streptococcus y Chromobacterium. 

Measurement of the -3 keV resonance in the reaction 13C(α,n)16O of importance in the s-process

The (13)C(α,n)(16)O reaction is the neutron source for the main component of the s-process, responsible for the production of most nuclei in the mass range 90</~A</~204. It is active inside the helium-burning shell in asymptotic giant branch stars, at temperatures </~10(8) K, corresponding to an energy interval where the (13)C(α,n)(16)O is effective from 140 to 230 keV. In this region, the astrophysical S(E)-factor is dominated by the -3 keV subthreshold resonance due to the 6.356 MeV level in (17)O, giving rise to a steep increase of the S(E)-factor. Notwithstanding that it plays a crucial role in astrophysics, no direct measurements exist inside the s-process energy window. The magnitude of its contribution is still controversial as extrapolations, e.g., through the R matrix and indirect techniques, such as the asymptotic normalization coefficient (ANC), yield inconsistent results. The discrepancy amounts to a factor of 3 or more right at astrophysical energies. Therefore, we have applied the Trojan horse method to the (13)C((6)Li,n(16)O)d quasifree reaction to achieve an experimental estimate of such contribution. For the first time, the ANC for the 6.356 MeV level has been deduced through the Trojan horse method as well as the n-partial width, allowing to attain an unprecedented accuracy in the (13)C(α,n)(16)O study. Though a larger ANC for the 6.356 MeV level is measured, our experimental S(E)-factor agrees with the most recent extrapolation in the literature in the 140-230 keV energy interval, the accuracy being greatly enhanced thanks to this innovative approach.

Agreement between ultrasonography and computed tomography in detecting intracranial calcifications in congenital toxoplasmosis

AIM

To evaluate the agreement between ultrasound (US) and computed tomography (CT) in detecting intracranial calcification in infants with congenital toxoplasmosis.

MATERIALS AND METHODS

Forty-four infants referred for investigation of congenital toxoplasmosis were prospectively evaluated, and the diagnosis was confirmed or ruled out by serological testing and by follow-up in the first year of life. The investigation protocol included cranial US and cranial CT, and examinations were conducted and interpreted by two radiologists blinded to the results of the other imaging test and to the diagnostic confirmation.

RESULTS

The diagnosis of congenital toxoplasmosis was confirmed in 33 patients, and agreement between US and CT findings was found in 31 of these cases. Both methods detected calcifications in 18 patients, and neither detected calcifications in 13 patients. Overall agreement was 94% and the kappa coefficient was 0.88 (95% confidence interval: 0.71, 1; p<0.001), which revealed almost perfect agreement between the two diagnostic methods.

CONCLUSION

In this study, US and CT demonstrated equal sensitivity in the detection of intracranial calcification in infants with congenital toxoplasmosis.

Th1/Th2 CD4+ T cell responses against NY-ESO-1 in HLA-DPB1*0401/0402 patients with epithelial ovarian cancer

The NY-ESO-1 antigen is expressed in a significant proportion of patients with epithelial ovarian cancer (EOC) and appears to be an ideal target for immunotherapy. In order to elucidate the nature of the HLA-DPB1*0401/0402 (DP4+)-restricted CD4+ immune response in patients with NY-ESO-1-expressing EOC, peripheral blood CD4+ T cells from HLA-DP4+ patients were stimulated with the NY-ESO-1 epitope 157-170 and tested for the release of type 1 (IFN-gamma) and type 2 (IL-5) cytokines in enzyme-linked immunospot assays. Of 14 DP4+ EOC patients who tested seronegative for NY-ESO-1, 3 patients had a detectable CD4+ T cell response to NY-ESO-1 epitope 157-170 by IFN-gamma ELISPOT assay. Six of 10 DP4+ EOC patients with serum antibodies to NY-ESO-1 had CD4+ T cell responses to NY-ESO-1 epitope 157-170 by IFN-gamma assay. Six patients had mixed Th1/Th2 CD4+ T cell responses to NY-ESO-1 epitope 157-170 regardless of their antibody response to NY-ESO-1. Four EOC patients had Th1 cells expressing IFN-gamma, but not IL-5. This suggests that the NY-ESO-1 epitope 157-170 stimulates both Th1 and Th2 type CD4+ T cell responses in EOC patients. These data suggest the NY-ESO-1 epitope 157-170 has a key role in the induction of cellular and humoral immune responses against NY-ESO-1-expressing EOC tumors. Our study supports the relevance of cancer vaccine trials with the NY-ESO-1 epitope 157-170 in HLA-DP4+ EOC patients with NY-ESO-1-expressing tumors and strategies to improve Th1-dominated tumor-reactive CD4+ T cell bias.

Cancer/testis antigen expression and autologous humoral immunity to NY-ESO-1 in gastric cancer

Gastric cancer has the highest mortality rate and the second-highest morbidity rate of all malignant tumors in China. Since cancer/testis (CT) antigens are expressed in various types of human tumors but generally not in normal tissue except for testis, they are promising antigens for cancer immunotherapy. NY-ESO-1, in particular, is the most immunogenic of the CT antigens. To study the feasibility of developing a CT antigen vaccine for gastric cancer, 101 gastric cancer samples were analyzed for the presence of NY-ESO-1 mRNA and that of 10 other CT antigen genes. Twelve out of 101 samples (11.9%) were found to be NY-ESO-1 mRNA-positive, 11 of them from advanced stage patients. In 7 of the 12 NY-ESO-1 mRNA-positive samples, the NY-ESO-1 protein was also detected by immunohistochemistry. An autologous humoral immune response to NY-ESO-1 was detected in 6 of 12 advanced stage NY-ESO-1 mRNA-positive patients, indicating that NY-ESO-1 is immunogenic in advanced stage gastric cancer. The serum from a patient with an NY-ESO-1 negative but LAGE-1 positive tumor was also found to be NY-ESO-1 antibody positive, possibly due to cross-reactivity between NY-ESO-1 and LAGE-1. All NY-ESO-1 mRNA-positive gastric cancer samples also expressed one to seven additional CT genes, revealing a tendency toward a clustered expression pattern, regardless of disease stage. About 74% of the samples expressed at least one CT antigen, most frequently MAGE-3 (41.6%). NY-ESO-1 and MAGE-3 are thus potential targets for a multivalent CT antigen vaccine.

SCP-1 cancer/testis antigen is a prognostic indicator and a candidate target for immunotherapy in epithelial ovarian cancer

SCP-1 is a novel tumor antigen that belongs to the growing family of cancer/testis (CT) antigens, and it is a potential target for immunotherapy. In an effort to determine the expression of SCP-1 in epithelial ovarian cancer (EOC), one-step RT-PCR was performed with RNA from epithelial ovarian tumor tissues and with two normal ovarian surface epithelial cell lines. We used immunohistochemistry (IHC) to investigate SCP-1 expression in paraffin-fixed EOC samples and ELISA to test sera from a subgroup of patients for SCP-1 antibody. SCP-1 was expressed in 15 out of 100 (15%) primary tumors, as determined by RT-PCR. The normal ovarian surface epithelial cell lines were negative for SCP-1 expression, as were a panel of other normal tissues. None of the patients whose tumors were determined to be SCP-1 positive by RT-PCR expressed the antigen by IHC or demonstrated a humoral immune response by ELISA. Tumors that expressed SCP-1 mRNA tended to have a higher grade than those that did not (P = 0.03). There was a significant decrease in survival time (P = 0.004) for patients with SCP-1 mRNA-positive tumors compared to those with SCP-1 mRNA-negative tumors [median 25 mo, 95% confidence interval (CI) 0-56 mo; and median 97 mo, CI 32-162 mo, respectively]. The present study shows that SCP-1 mRNA expression in patients with EOC is associated with a poorer chance of survival. These findings imply that further evaluation of SCP-1 as a potential target for vaccine therapy in EOC is warranted.

Vaccine-induced CD4+ T cell responses to MAGE-3 protein in lung cancer patients

MAGE-3 is the most commonly expressed cancer testis Ag and thus represents a prime target for cancer vaccines, despite infrequent natural occurrence of MAGE-3-specific immune responses in vivo. We report in this study the successful induction of Ab, CD8(+), and CD4(+) T cells in nonsmall cell lung cancer patients vaccinated with MAGE-3 recombinant protein. Two cohorts were analyzed: one receiving MAGE-3 protein alone, and one receiving MAGE-3 protein with adjuvant AS02B. Of nine patients in the first cohort, three developed marginal Ab titers and another one had a CD8(+) T cell response to HLA-A2-restricted peptide MAGE-3 271-279. In contrast, of eight patients from the second cohort vaccinated with MAGE-3 protein and adjuvant, seven developed high-titered Abs to MAGE-3, and four had a strong concomitant CD4(+) T cell response to HLA-DP4-restricted peptide 243-258. One patient simultaneously developed CD8(+) T cells to HLA-A1-restricted peptide 168-176. The novel monitoring methodology used in this MAGE-3 study establishes that protein vaccination induces clear CD4(+) T cell responses that correlate with Ab production. This development provides the framework for further evaluating integrated immune responses in vaccine settings and for optimizing these responses for clinical benefit.

Frequency of NY-ESO-1 and LAGE-1 expression in bladder cancer and evidence of a new NY-ESO-1 T-cell epitope in a patient with bladder cancer

Cancer-testis (CT) antigens are ideal vaccine targets since their expression is restricted in adult tissues to testicular germ cells and a subset of cancers. The frequency of expression in transitional cell carcinomas (TCCs) of NY-ESO-1, the most immunogenic CT antigen to date, and its closely related gene LAGE-1 was studied. NY-ESO-1 and LAGE-1 antigen expression were found to occur frequently in high-grade TCC tumors. On an MSKCC IRB-approved protocol, 68 patient specimens were collected prospectively at the time of transurethral resection or cystectomy, of which 43 were read pathologically as high-grade tumors (pCIS, pTaG3, pT1, pT2, pT3, and pT4), 8 as low-grade tumors (pTaG1, pTaG2), and 17 as disease-free samples. These 68 samples were analyzed by immunohistochemistry (IHC) and/or RT-PCR. There were also an additional 53 paraffin-embedded specimens studied retrospectively by IHC, of which 39 were high-grade tumors and 14 were low-grade tumors. Cumulatively, our data indicate that NY-ESO-1 and/or LAGE-1 are expressed in 39/82 (48%) high-grade TCC and 3/22 (14%) low-grade TCC samples when analyzed by RT-PCR and/or IHC. Immunological assessment of these patients' sera identified one patient, whose tumor homogeneously expressed NY-ESO-1, which had detectable antibodies against NY-ESO-1 and LAGE-1. Further analysis of this patient, who remains clinically without evidence of disease 24 months after cystectomy for high-grade pT4 disease, revealed T-cell immunity against NY-ESO-1. This patient's T-cell response was determined to be specific for a new NY-ESO-1 epitope, p94-102, in the context of HLA-B35.

NY-ESO-1 and LAGE-1 cancer-testis antigens are potential targets for immunotherapy in epithelial ovarian cancer

Cancer-testis (CT) antigens are expressed in a variety of cancers, but not in normal adult tissues, except for germ cells of the testis, and hence appear to be ideal targets for immunotherapy. In an effort to examine the potential of NY-ESO-1 and LAGE-1 CT antigens for immunotherapy in epithelial ovarian cancer (EOC), we examined the expression of these antigens by reverse transcription-PCR (RT-PCR) and immunohistochemistry (IHC) in a large panel of EOC tissues and cell lines. Sera from a subgroup of the patients were tested for NY-ESO-1/LAGE-1 antibody by ELISA. The data indicated that four ovarian cancer cell lines were positive for one or both CT antigens. Expression of NY-ESO-1 in EOC was demonstrated by RT-PCR and/or IHC in 82 of 190 (43%) specimens. NY-ESO-1 expression by IHC ranged from homogeneous to heterogeneous pattern. LAGE-1 mRNA expression was present in 22 of 107 (21%) tumor tissues. Overall, the expression of either NY-ESO-1 or LAGE-1 mRNA was present in 42 of 107 (40%) EOC specimens and coexpression of both antigens was demonstrated in 11% of specimens. Antibody to NY-ESO-1/LAGE-1 was present in 11 of 37 (30%) patients whose tumors expressed either NY-ESO-1 or LAGE-1. Detectable antibodies were present for up to 3 years after initial diagnosis. Although there was no statistically significant relation between expression of NY-ESO-1/LAGE-1 antigen and survival, the data showed aberrant expression of NY-ESO-1 and LAGE-1 by IHC/RT-PCR in a significant proportion of EOC patients. These findings indicate that NY-ESO-1 and LAGE-1 are attractive targets for antigen-specific immunotherapy in EOC.

Recombinant antigen expression on yeast surface (RAYS) for the detection of serological immune responses in cancer patients

The serological analysis of antigens by recombinant expression cloning (SEREX) has identified a multitude of new tumor antigens in many different tumor entities. These antigens can be grouped into different classes according to their specificities, with cancer/testis antigens appearing to be the most attractive candidates for vaccine development. The observation that CD8 and CD4 T-cell responses against cancer/testis antigens such as NY-ESO-1 correlate with the presence of specific antibodies demonstrates the importance of serological monitoring patients participating in vaccine trials. However, all serological assays available (Western blot, phage display and ELISA) are hampered by the fact that the protein cannot be analyzed in its natural conformation. We have thus developed a yeast display system where the antigen is expressed on the yeast surface (RAYS), allowing for a more natural folding of the protein. To validate this approach we displayed the A33 colorectal cancer antigen on the yeast cell surface and demonstrated specific binding by an A33 monoclonal antibody recognizing a conformation-dependent epitope on the A33 antigen. We then compared RAYS with the more commonly used ELISA and Western blot serological monitoring methods by analyzing 50 sera from cancer patients with known NY-ESO-1 antibody status and 10 sera from patients with unknown SSX2 antibody status in a blind fashion. RAYS appears at least equivalent to both ELISA and Western blotting for the monitoring of antibodies against NY-ESO-1 as regards specificity and sensitivity, while antibodies against SSX2 were detected more frequently by RAYS than by ELISA or phage display.

[Unilateral renal agenesis associated with pelvic renal ectopy]

OBJECTIVE

To describe a rare case of right renal agenesia and left pelvic ectopy. To our knowledge, only 10 such cases have been reported in the world literature.

METHODS

A 76-year-old male patient who consulted for irritative prostatic syndrome is described. Patient evaluation included IVP and CT.

RESULTS

IVP revealed the absence of the right kidney in addition to an anomalous position of the left kidney. The foregoing findings were confirmed by CT.

CONCLUSION

This uncommon congenital anomaly is essentially asymptomatic and is generally diagnosed in infants through its complications. In the case described herein, however, this anomaly had been incidentally detected during IVP and CT assessment of a 76-year-old patient who had consulted for irritative prostatic syndrome.

Basic fibroblast growth factor as a biochemical marker of exercise-induced ischemia

BACKGROUND

Basic fibroblast growth factor (bFGF) is a mitogenic polypeptide that demonstrates enhanced expression and promotes angiogenesis in animal models of myocardial ischemia and infarction. Elevated levels of bFGF are present in the urine of humans with metastatic tumors, but its expression in human myocardial ischemia is unknown. Thus, we sought to determine whether urine levels of bFGF are altered by exercise-induced ischemia in humans.

METHODS AND RESULTS

Eighty-six patients underwent exercise thallium studies for evaluation of anginal symptoms. Urine levels of bFGF (corrected for urine creatinine) were determined by ELISA immediately before and between 2 and 4 hours after exercise. The change in urine bFGF level was compared between 43 patients with and 43 patients without exercise-induced ischemia. Patients with ischemia had an increase in urine bFGF compared with nonischemic patients (1052 +/- 245 versus -278 +/- 130 pg/g creatinine, P < .0001). Exercise, demographic, and clinical variables were assessed and analyzed for possible effect on bFGF response to exercise. By univariate analysis, a history of hypertension was negatively associated with a change in bFGF level (P < .05). No other variables were associated. By multivariate analysis, only bFGF response (P < .001) and age (P < .05) were independently related to exercise-induced ischemia.

CONCLUSIONS

Significantly increased levels of bFGF are detected in the urine within hours of exercise-induced ischemia. Further studies are warranted to determine whether bFGF might serve as a useful circulating marker of myocardial ischemia in humans.

Concentration-time profiles of oxytetracycline in blood, kidney and liver of tench (Tinca tinca L) after intramuscular administration

Oxytetracycline (OTC) is a widely-used antibiotic in several animal species. The Food and Drug Administration allows OTC to be used in fish intended for human food, but there is limited kinetics data available. We studied OTC concentrations in plasma, kidney and liver in tenches (Tinca tinca L) after im administration using HPLC. Concentrations were fit to a monocompartment open model by extended least squares regression analysis using the MULTI (ELS) computer program. Peaks of OTC concentrations (Cmax) occurred at 4 h for blood and kidney and 72 h for liver and were 134.1 micrograms/mL, 129.8 micrograms/g and 333.4 micrograms/g, respectively. There was a high correlation (r = 0.9448) between blood and kidney concentrations and less between blood and liver. Concentrations were statistically different for each system. The blood OTC concentrations were higher than renal concentrations 92% of the time and were higher than hepatic concentrations 29% of the time. The plasma OTC half-life (21.2 h) was longer than in homeothermic species. The tench liver maintains considerable OTC residues and may affect food products derived from that organ.

Left atrial appendage function and thrombus formation in atrial fibrillation-flutter: a transesophageal echocardiographic study

OBJECTIVES

The purpose of this study was to investigate left atrial appendage size, function and thrombus prevalence in patients with atrial "fibrillation-flutter."

BACKGROUND

Thrombus formation and peripheral embolization in atrial fibrillation are related to left atrial appendage dysfunction. Embolization occurs less frequently in atrial flutter. It is not known whether the atrial appendage in fibrillation-flutter, which has an intermediate appearance on the surface electrocardiogram (ECG), has distinct characteristics that could affect thrombus formation.

METHODS

Sixty-one patients with atrial tachyarrhythmias underwent transesophageal echocardiographic examination of the left atrial appendage. Appendage area, peak emptying velocity and the presence of thrombus and spontaneous echo contrast were determined. The results for 14 patients with fibrillation-flutter (based on ECG fibrillatory wave characteristics) were compared with those for 30 patients with atrial fibrillation and 17 patients with atrial flutter.

RESULTS

Both fibrillation-flutter and atrial fibrillation were associated with chaotic appendage flow patterns with similarly low peak emptying velocities (18 +/- 8 and 17 +/- 10 cm/s, mean +/- 1 SD, respectively). Atrial flutter was associated with a regular pattern of appendage contraction and a significantly higher peak emptying velocity (42 +/- 18 cm/s, p < 0.0001). Mean appendage area was similar for fibrillation-flutter and fibrillation (6.3 +/- 2.2 and 6.7 +/- 2.1 cm2, respectively) but was significantly smaller for atrial flutter (5.3 +/- 1.4 cm2, p < 0.05). The prevalence of left atrial appendage thrombus was similar for fibrillation-flutter and atrial fibrillation (40% and 29%, respectively), whereas no patient with atrial flutter had a thrombus (p < 0.05). Similarly, the presence of spontaneous echo contrast was higher for fibrillation-flutter (50%) and atrial fibrillation (40%) than for atrial flutter (6%, p < 0.05).

CONCLUSIONS

Left atrial appendage size and function in atrial fibrillation-flutter are indistinguishable from those of typical atrial fibrillation, and the frequency of thrombus and spontaneous echo contrast is similarly high. This is in contrast to atrial flutter, which is characterized by a smaller, more contractile left atrial appendage and a lower frequency of thrombus and spontaneous echo contrast.

Partial intercalation with DNA of peptides containing two aromatic amino acids

The interactions with DNA of tetrapeptide amides containing lysine at the N-terminal position and aromatic amino acids at the second and fourth positions (Ala at position three), 1-6, have been investigated by nmr, CD, and viscometric methods. Tetrapeptides with N-terminal lysine and a single aromatic amino acid, 7-10, were investigated as controls. Significant decreases in DNA viscosity occurred on addition of 7, with the aromatic group at the second position, but not with any of the other single aromatic amino acid peptides. All of the tetrapeptides with two aromatic groups caused DNA viscosity decreases which were two to three times larger than with 7. Peptides with p-nitrophenylalanine (p-NO2Phe) as the aromatic group were synthesized for nmr studies because of its simpler aromatic nmr spectrum relative to Phe. Large upfield shifts of the aromatic proton signals were obtained when the amino acid in the second position was L-p-NO2Phe, and the fourth position contained either p-NO2Phe or Phe. Such peptides also caused the largest DNA viscosity decreases on complex formation. Smaller upfield shifts of the aromatic signals were obtained when the amino acid in the second position was L-Phe or a D isomer of Phe or p-NO2Phe. With all peptides, larger upfield nmr shifts were obtained with heat-denatured, recooled DNA than with native DNA under the same conditions. As with nmr, CD results are quite different for the peptides with L and D amino acids at the second position. All of the results can be interpreted in terms of a model in which lysine interacts stereospecifically with the backbone in a DNA double helix and the aromatic group at the second position stacks strongly with the base pairs when the amino acid is an L isomer. The aromatic group at the fourth position can also interact with the base pairs, but primarily through a sideways stacking of the aromatic group with base pairs for either L or D isomers. Because of covalent constraints on the separation distance for the two aromatic groups in the tetrapeptides, they must stack on opposite sides of the same base pair in violation of the neighbor exclusion principle observed with classical intercalators. This stacking at the same base pair no doubt accounts for the larger viscosity decreases in DNA with the peptides containing two aromatic groups relative to those with a single aromatic group.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of metal in liver alcohol dehydrogenase catalysis. Spectral and kinetic studies with cobalt-substituted enzyme

The kinetic and spectral properties of native and totally cobalt-substituted liver alcohol dehydrogenase have been compared. Based on titrimetric determinations of enzyme active site concentration, the turnover number at pH 7.0 for cobalt enzyme was the same as for native enzyme. At pH 10, however, the turnover number was slower for cobalt-substituted enzyme, 3.14 s-1 as compared with 4.05 s-1 for native enzyme. A comparison between native and totally cobalt-substituted enzyme showed a blue-shifted enzyme-NADH double difference spectrum and a splitting and red-shifted enzyme-NAD+-pyrazole double difference spectrum in the near-ultraviolet. The 655-nm peak of the cobalt-substituted enzyme was perturbed by the formation of enzyme-NADH binary complex, enzyme-NAD+-trifloroethanol ternary complex, and enzyme-NAD+ binary complex formation. At pH 7.0, the only observable step in the reaction sequence with a significantly different rate constant for cobalt enzyme was the catalytic hydrogen-transferring step. The rate constant for this step is 92 s-1 for totally cobalt-substituted enzyme as compared with 138 s-1 for native liver alcohol dehydrogenase. The results of this study indicate that zinc is involved in catalysis alcohol and NADH.