Perisaccadic occipital EEG changes quantified with wavelet analysis.
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Electroencephalography↗
Biomedical subjects
M Avitable
Publications and source records attributed to M Avitable.
High grade adenocarcinoma of prostate in smokers of ethnic minority groups and Caribbean Island immigrants.
The degree of differentiation of 670 blacks and white patients treated from 1980-1990 for curative and palliative external beam radiation therapy and surgery at State University of New York Health Science Center at Brooklyn and Kings County Hospital were analyzed retrospectively, stratified according to race, age, smoking, and grade. In addition stage, birth place and median survival were also analyzed. Overall mean age was 69 years (Std. Dev. 8.97). 69% were blacks and 27.8% were whites. 65.4% were smokers and 34.6% were non-smokers. Smokers had high incidence of more invasive and high grade adenocarcinoma of prostate (p < or = 0.00005) compared to control group (non-smokers with prostate carcinoma). Statistically significant difference was found in the degree of differentiation of carcinoma of prostate in smokers compared to non-smokers. Smokers had 15.04% well, 27.07% moderate, and 57.89% poorly differentiated adenocarcinoma compared to non-smokers in which 37.1% were well, 45.16% moderate, and 17.74% poorly differentiated cancer of prostate (p < or = 0.00005). Sixty-three percent blacks and 40.16% whites had Stage D cancer (p < or = 0.00005). 68.3% smokers and 53.3% non-smokers had Stage D cancer (p = 0.01). Overall median survival for blacks was 74.04 months compared to whites of 115.73 months (p < or = 0.00005).
Adenocarcinoma↗
Conformational effects of amino acid substitutions at positions 10, 12, and 13 in the P21 protein.
Substitutions of amino acids for Gly 12 or Gly 13 in the ras oncogene-encoded P21 proteins have been demonstrated to produce unique structural changes in these proteins that correlate with their ability to produce cell transformation. For example, the P21 proteins with Arg 12 or Val 13 are both known to be actively transforming. Recent site-specific mutagenesis experiments on the transforming Arg 12 protein have found that the substitution of Val for Gly 10 has no effect on transforming activity whereas the substitution of Val for Gly 13 led to a loss of transforming activity. In this study, we examine the structural effects of these substitutions on the amino terminal hydrophobic decapeptide (Leu 6-Gly 15) of P21 using conformational energy analysis. The results show that the transforming proteins with Gly 10 and Arg 12 or Val 10 and Arg 12 can both adopt the putative malignancy-causing conformation, whereas, for the nontransforming protein with Arg 12 and Val 13, this conformation is energetically disallowed. These results further support the theory that due to structural changes the transforming P21 proteins are unable to bind to some regulatory cellular element which may be the recently identified binding protein responsible for the induction of increased GTPase activity in normal P21 compared with transforming mutants.
Amino Acids↗
Conformation of the metastasis-inhibiting laminin pentapeptide.
The binding of cancer cells to the basement membrane glycoprotein laminin appears to be a critical step in the metastatic process. This binding can be inhibited competitively by a specific pentapeptide sequence (Tyr-Ile-Gly-Ser-Arg) of the laminin B1 chain, and this peptide can prevent metastasis formation in vivo. However, other similar pentapeptide sequences (e.g., Tyr-Ile-Gly-Ser-Glu) have been found to be much less active in metastasis inhibition, raising the possibility that such amino acid substitutions produce structural changes responsible for altering binding to the laminin receptor. In this study, conformational energy analysis has been used to determine the three-dimensional structures of these peptides. The results indicate that the substitution of Glu for the terminal Arg produces a significant conformational change in the peptide backbone at the middle Gly residue. These results have important implications for the design of drugs that may be useful in preventing metastasis formation and tumor spread.
Amino Acids↗
Conformational effects of the substitution of Arg for Gly 13 in the ras oncogene-encoded P21 protein.
The effect of the substitution of Arg for Gly 13 on the structure of the transforming region decapeptide (Leu 6-Gly 15) of the ras oncogene encoded P21 protein has been investigated using conformational energy analysis. A human malignancy has been identified that contains a ras gene with a single mutation in the thirteenth codon such that the encoded protein would have Arg substituted for Gly at this position, and transfection of cells in culture with this gene results in malignant transformation. Conformational analysis demonstrates that the Arg 13 decapeptide adopts a conformation identical to that for other peptides with substitutions at position 13 (Asp 13, Val 13) from transforming proteins that is distinctively different from that for peptides (Gly 13, Ser 13) from normal, nontransforming proteins. This is found to be an indirect effect resulting from changes in the conformation of Gly 12 produced by substitutions at position 13. These results are consistent with recent analysis of crystallographic data of proteins on conformational preferences for glycine in tripeptide sequences.
Arginine↗
Pharmacokinetics of sufentanil in patients undergoing renal transplantation.
Renal failure and chronic haemodialysis are often associated with alterations in fluid status and plasma proteins. These changes, in turn, may result in pharmacokinetic alterations in affected patients. The purpose of this study was to investigate the pharmacokinetics of sufentanil in chronic renal failure patients undergoing kidney transplantation. Ten male patients were studied. Following induction of anaesthesia each patient received sufentanil 2.0 micrograms.kg-1 IV with subsequent serial plasma sampling for drug measurement from one to 360 minutes. A biexponential equation provided the best fit of the sufentanil concentration data with mean +/- SEM distribution (alpha) and elimination (beta) half-lives of 2.9 +/- 1.3 and 176 +/- 87 minutes, respectively. The mean Vc and Vd beta values were 0.15 +/- 0.05 L.kg-1 and 0.85 +/- 0.16 L.kg-1, respectively; plasma drug clearance was 11.5 +/- 3.7 ml.kg-1.min-1. Mean values for K10, K12 and K21 were 0.15 +/- 0.06.min-1, 0.4 +/- 0.14.min-1 and 0.1 +/- 0.04.min-1, respectively. With the exception of Vd beta, these pharmacokinetic values are similar to those reported in previous studies in general surgical, elderly and burn patients. The Vd beta values observed in this study may have resulted from alterations in drug distribution or elimination following revascularization of the implanted kidneys. Nevertheless, it appears that modification of sufentanil doses is unnecessary in chronic renal failure patients undergoing renal transplantation.
Adult↗
Structure of the carboxyl terminus of the RAS gene-encoded P21 proteins.
The three-dimensional structures of the carboxyl-terminal regions of the P21 protein products of the human Harvey (Ha), Kirsten (KiA and KiB), and neuroblastoma (N) RAS oncogenes and various mutants have been determined by using conformational energy analysis. The carboxyl-terminal region of P21 has been strongly implicated in the binding of the protein to the inner surface of the plasma membrane without which the protein is inactive. The only invariant residue in this region is Cys-186, which is necessary for the post-translational addition of palmitic acid. The surrounding sequences of the active native proteins differ considerably. Nevertheless, certain amino acid substitutions in this region are known to eliminate membrane binding and protein activity, suggesting that there is a conserved common structural feature in this region in the native proteins that is disrupted in the mutant proteins. Conformational energy analysis shows that the four native P21 proteins have a common structure in the form of an alpha-helix for the terminal pentapeptide. A mutant, pBW277, that fails to bind to the membrane and is inactive cannot adopt an alpha-helical structure in this region because of a proline at position 188. Another mutant, pBW766, that retains membrane binding and activity, on the other hand, retains the preference for an alpha-helical conformation in the terminal pentapeptide. These findings suggest that, despite various amino acid sequences in this region, the carboxyl-terminal pentapeptides of the P21 proteins form a distinctive structural domain that must have an alpha-helical structure for membrane binding and intracellular activity.
Cell Membrane↗
On the biologically active structures of cholecystokinin, little gastrin, and enkephalin in the gastrointestinal system.
The biologically active conformations of a series of four peptides [four cholecystokinin (CCK)-related peptides and enkephalin] in their interactions with gastrointestinal receptors have been deduced using conformational computational analysis. The two peptides that interact exclusively with peripheral-type CCK receptors are the heptapeptide COOH-terminal fragment from CCK (CCK-7) and the analogous sequence from cerulein (CER-7) in which threonine replaces the methionine proximal to the NH2 terminus. The two peptides that interact exclusively with the gastrin receptor in the stomach are the active COOH-terminal fragment of little gastrin and the COOH-terminal tetrapeptide sequence common to all of these peptides, CCK-4. We find that preferred conformations for the peripherally active peptides CCK-7 and CER-7 are principally beta-bends, whereas little gastrin and CCK-4 are fundamentally helical. In the class of lowest energy structures for both CCK-7 and CER-7, the aromatic rings of the tyrosine and phenylalanine lie close to one another whereas the tryptophan indole ring points in the opposite direction. This structure is superimposable on the structures of a set of rigid indolyl benzodiazepine derivatives that interact with complete specificity and high affinity with peripheral CCK receptors further suggesting that the computed beta-bends are the biologically active conformation. The biologically active conformation for CCK-4 and the little gastrin hexapeptide has also been deduced. By excluding conformations common to CCK-7 and CCK-4, which do not bond to each other's receptors, and then by selecting conformations in common to CCK-4 and the gastrin-related hexapeptide, which do bind to each other's receptors, we deduce that the biologically active conformation at the gastrin receptor is partly helical and one in which the indole of tryptophan and the aromatic ring of phenylalanine are close to one another while the methionine and aspartic acid side chains point in the opposite direction. These major differences in preferred structures between the common CCK-7/CER-7 peptides and the common CCK-4/little gastrin peptides explain the mutually exclusive activities of these two sets of peptides. We have observed that [Met]enkephalin strongly antagonizes the action of the naturally occurring peripherally active CCK-8 (CCK-7 with an NH2-terminal aspartic acid residue added). The computed lowest energy structures for this opiate peptide closely resemble key features of the computed CCK-7/CER-7 structure, further supporting the proposed structure.
Amino Acid Sequence↗
Conformational effects of substituting amino acids for glutamine-61 on the central transforming region of the P21 proteins.
The low-energy conformations for a series of peptides based on the sequence of the ras P21 protein from position 55 to position 67 have been computed using conformational energy analysis. These sequences differed at position 61 and contained Gln, Pro, Leu, Lys, and Arg at this position. P21 proteins with Gln, Glu, or Pro at this position do not cause cell transformation at normal levels of expression; proteins with substitutions of at least 14 other amino acids at this position (Leu, Lys, and Arg having been found in tumors in place of the normally occurring Gln-61) do cause malignant transformation of cells in culture. We find that the segments of residues 55-67 from the nontransforming proteins (Gln- or Pro-61) adopt a structure that is energetically unfavorable for the same segment with Leu, Lys, or Arg at position 61. The critical feature of this structure is an alpha-helix from residues 62 to 68. Residue 61 (Gln or Pro) adopts an extended conformation. On the other hand, the segment from transforming proteins can adopt two structures, one all alpha-helical from residue 61 to residue 68 and the other a less-regular, higher-energy structure. The segments from the normal protein can adopt the all alpha-helical structure, a finding that can explain the fact that elevated intracellular levels of the normal protein also cause cell transformation. The results of the calculations suggest that specific changes in the structure of this region can account for the oncogenic effect of the proteins in which substitutions occur.
Amino Acid Sequence↗