Measurement of activity in older adults: reliability and validity of the Step Activity Monitor.

The purpose of this study was to test the reliability and validity of the Step Activity Monitor (SAM) when used with older adults. A total of 30 subjects with a mean age of 86 +/- 6.1 participated in the study. Sixty one-minute walks were measured with the SAM, and two observers visually counted steps. Four participants wore the SAM for 6 to 48 hours and maintained activity diaries. The intraclass correlation for the SAM recordings was R = .84. There was an overall step counting accuracy of 96%. The diaries supported the SAM data for those who wore the SAM for extended periods. The SAM is an easy to use, comfortable, valid, and reliable measure of activity in older adults and particularly may be useful to triangulate measurement of activity in these individuals.

A binding study of phospholipase A2 with lecithin, lysolecithin and their tetrahedral intermediates using molecular modeling.

We used molecular modeling to examine the binding of 1,2-dioctanoyl-sn-glycero-3-phosphocholine (a lecithin), 1-octanoyl-sn-glycero-3-phosphocholine (a lysolecithin) and their tetrahedral intermediates in the catalytic site of phospholipase A2 (PLA2). We performed energy minimization on each complex, computed the binding energy, determined the relative binding energy among the complexes and calculated the difference in inter- and intramolecular energies of the components in the complexes. We found that the calculated orientation of the sn-1 ester bond of lysolecithin in the active site is similar to that of the sn-2 ester bond in lecithin, thus permitting PLA2 to hydrolyze lysolecithin using the same mechanism as it uses to hydrolyze lecithin. On the other hand, the binding of lecithin is energetically more favorable by 4.5 kcal/mol than the binding of lysolecithin to the enzyme, and the binding of the lecithin tetrahedral intermediate is also energetically more favorable by 19.7 kcal/mol than the binding of the lysolecithin tetrahedral intermediate to the enzyme, which explains why lecithin is a better substrate than lysolecithin in the catalytic site. These results indicate that the activation energy for the hydrolysis of lysolecithin is higher than that for lecithin, consistent with the observed slower rate for the hydrolysis of lysolecithin.

Calculations of the phi-psi conformational contour maps for N-acetyl alanine N'-methyl amide and of the characteristic ratios of poly-L-alanine using various molecular mechanics forcefields.

We generated phi- psi conformational energy contour maps for the N-acetyl alanine N'-methyl amide using the molecular mechanics forcefields AMBER, AMBER3, BIO85, CFF91, CVFF, MM2, MM3, MM+, AND SYBYL. With MM2, MM3, and MM+ we used a dielectric constant of epsilon = 1.5, the default effective value for these forcefields. With the other forcefields we used epsilon = 1 and 4, except with SYBYL, which, in Spartan 3.1, has no electrostatic term. All forcefields yielded the C7eq conformation as a low-energy minimum or the global minimum. Most of the forcefields also yielded a minimum-energy conformation in the C5, alpha R, and alpha L regions of the phi-psi contour map. Fewer of the forcefields yielded a minimum in the C7ax region; however, adiabatic relaxation frequently lowered the relative energy of this region. Based on the appearance of the phi-psi maps, the following pairs of forcefields were broadly similar (but not identical) to each other but dissimilar to the other pairs: AMBER3 and AMBER, BIO85 and CHARMM, MM+ and MM2, SYBYL and ECEPP, and CFF91 and MM3. We used the data from the phi-psi contour maps to compute the characteristic ratio of poly-L-alanine. Most of the computed values deviated significantly from the experimental value. Only the computed characteristic ratio of CFF91 without adiabatic relaxation at epsilon = 4 and MM3 without adiabatic relaxation at epsilon = 1.5 agreed with the experimental value.

Cooperative education: an alternative level I fieldwork.

The cooperative education program offered at the University of North Dakota is based on programs offered at other universities across the nation. Rewards of cooperative education programs are many, and they benefit students, universities, and sponsors alike. In addition to easing the costs of a university education, planning cooperative education experiences as part of the curriculum allows students to develop, practice, and receive feedback on the necessary professional skills vital to their success as occupational therapists. Universities and sponsors benefit from enhanced relationships and lay the foundation for joint ventures as educators and researchers. Further research is needed to evaluate specific outcomes related to the use of cooperative education in the training of occupational therapists. This research should address issues that include evaluation tools, students' perspectives, and employers' satisfaction with the program.

Conformational energy analysis of the pentapeptide Ac-Arg-Asn-Cys-Tyr-Asn-NMA from alpha 1-purothionin.

Conformational energy analyses were carried out on the pentapeptide RNCYN (Ac-Arg-Asn-Cys-Tyr-Asn-NMA) and on related peptides. RNCYN is a highly conserved amino acid sequence in thionins and viscotoxins. The conformation of the pentapeptide was calculated to be an amphipathic alpha-helix, with the tyrosine and cysteine on the nonpolar side of the helix and the arginine and both asparagines on the polar side. Our results are inconsistent with the conformation determined using the Chou-Fasman prediction method, but are consistent with the conformation determined experimentally (using n.m.r.) for this pentapeptide sequence in alpha 1-purothionin.

Conformational energy analysis of the chemotactic tripeptide formyl-Met-Leu-Phe and three analogs.

Conformational energy analyses were carried out on the chemotactic tripeptide fMLF (CHO-Met-Leu-Phe) and three analogs fALF (CHO-Ala-Leu-Phe). fMF (CHO-Met-Phe), and MLF (H-Met-Leu-Phe). A near-folded or puckered conformation predominates in all four peptides. The calculated average end-to-end distance R of each of the peptides is 7.4 A, 7.6 A, 7.0 A, and 7.3 A, respectively (where bends have R less than or equal to 7 A and extended structures have R approximately 10.5 A). The puckered conformation calculated for fMLF is similar to that determined experimentally for fMLF in nonpolar solvents and in the protein receptor. The results suggest that maximum chemotactic activity of the peptides depends on a combination of the chemical structure (the presence of N-formyl-methionine) and backbone conformation (C7conformation of the first amino acid residue).

Conformational energy analysis of melanostatin.

Conformational energy calculations were carried out on the hypothalamic hormone melanostatin, a tripeptide with the primary structure H-L-Pro-L-Leu-Gly-NH2. The calculated lowest energy conformation was a type II beta bend, very similar to that reported in an X-ray crystal study. This conformation, however, was only one of 109 low-energy structures (less than or equal to 3 kcal/mol above the global minimum), indicating that the molecule in solution exists as an ensemble of conformations and is very flexible, in agreement with relaxation data from n.m.r. measurements. A statistical analysis yielded an average end-to-end distance of 6.8 A and a bend probability of 0.62, suggesting that, in nonpolar solvents, bend structures predominate within the statistical ensemble. The statistical analysis, however, also yielded a probability of only 0.11 for the occurrence of a 4 leads to 1 hydrogen bond. Hence, the calculations show that, although bend conformations predominate, bends would be difficult to observe in solution if the experiments were designed only to detect 4 leads to 1 hydrogen bonds.

Carbon monoxide poisoning.

Carbon monoxide poisoning has received little attention in th pediatric literature, although it is not uncommon in children. With the advent of alternative energy sources, such as woodburning stoves, one might predict an increase in its incidence over the next few years. Carbon monoxide poisoning is well described in the adult medical, surgical, neurologic, and psychiatric literature. It can cause a severe encephalopathy and have cardiovascular, pulmonary, muscular, renal, cutaneous, visual, and auditory manifestations. In this review a case of severe carbon monoxide poisoning with complications is presented.

Conformational characteristics of the N-acetyl-N'-methylamides of the four (Lys, Tyr) dipeptides.

The conformational properties of the N-acetyl-N'-methylamides of the dipeptides lysyl-lysine, lysyl-tyrosine, tyrosyl-lysine, and tyrosyl-tyrosine were studied by means of conformational energy calculations, by n.m.r. measurements in deuterated dimethylsulfoxide, and by circular dichroism in water, methanol, dioxane-water, and trifluoroethanol. Since these four dipeptides occur occasionally as bends in proteins, it was of interest to see whether short-range interactions, acting within the terminally blocked dipeptides, are sufficient to stabilize bend conformations significantly over other conformations. It was found that the four dipeptides exist as ensembles of conformations in solution. Therefore, it appears that longer-range interactions, such as those present in proteins, are required if bend conformations of these dipeptide sequences are to exist as stable conformations. Three of the dipeptides behave rather similarly. Both the CD and the n.m.r. experiments and computations indicate that the fourth (Lys-Tyr) differs from the others. It has a preference for compact conformations that appear to be stabilized by strong favorable interactions, primarily hydrogen bonds, between the tyrosyl and the lysyl side chains. The computations suggest that the presence of these interactions, and hence the existence of preferred conformations, is strongly solvent-dependent, and that these interactions are weakened in aqueous solution.

Local interactions in bends of proteins.

Calculated probabilities of bend formation in 47 amino acid sequences of N-acetyl-N'-methylamide dipeptides, determined from a statistical mechanical analysis using empirical conformational energies, were compared with the observed fraction of bends formed in the same 47 dipeptide sequences in the x-ray structures of 20 globular proteins. Agreement between the calculated and observed fraction of bends was found for 26 dipeptides, suggesting that, for those particular dipeptide sequences, local interactions dominate over long-range interactions in determining conformational preference. Seven dipeptide sequences, all of which contained a Gly residue, had a significantly higher calculated than observed bend preference, indicating the strong influence of long-range and/or solvent interactions in those sequences. Of the 14 sequences for which the calculated was significantly less than the observed bend fraction, 13 dipeptide sequences contained at least one polar residue (Ser, Asn, or Asp) and/or an aromatic residue (Phe or Tyr), suggesting that solvent effects may play an important role in dictating the conformation in these sequences. The analysis of dipeptide sequences in the twenty globular proteins also indicated that the 4 leads to 1 hydrogen bond is not a dominant factor in stabilizing bends in proteins, and that most dipeptide sequences are capable of forming several types of bend conformations.

Structures of enzyme-substrate complexes of lysozyme.

Conformational energy calculations were used to determine the binding structures of two oligosaccharides (GlcNAc)(n), in which n = 5 and 6, in the rigid active site of lysozyme (mucopeptide N-acetylmuramoylhydrolase, EC 3.2.1.17). Starting with the lowest energy binding structures of (GlcNAc)(4) as determined in a previous publication, we added a fifth GlcNAc residue to this tetramer in three different conformations, corresponding to the left-handed and right-handed helical structures and an intermediate structure, and the energy of each complex was minimized. The most stable binding conformation of the fifth residue of the pentamer was closest to the left-handed helical one. During energy minimization, the fourth residue of the pentamer moved from its initial position near the surface of the active site farther into the active site cleft at binding site D. Binding structures of (GlcNAc)(6) were then examined by addition of a residue to the lowest energy structure of (GlcNAc)(5), and it was found that the sixth residue of the hexamer binds in a conformation again close to the left-handed helical one. Stable binding regions of the rigid active site for the fifth and sixth residues were found to be near arginyl 45 and asparaginyl 46, on the opposite side of the active site cleft from arginyl 114. When the calculated structure of the lysozyme-(GlcNAc)(4) complex (used here as the starting structure for addition of the fifth and sixth residues) is compared with recent experimental data, it is found that the calculated structure is a reasonable one. Of all binding regions available to the saccharide residues, the C site binds GlcNAc with the lowest energy, in agreement with experiments.

Conformational analysis of the 20 naturally occurring amino acid residues using ECEPP.

Conformational energy calculations using ECEPP (Empirical Conformational Energy Program for Peptides) were carried out on the N-acetyl-N'-methylamides of the 20 naturally occurring amino acids. Minimum-energy conformations were located, and the relative conformational energy, librational entropy, and free energy each minimum were calculated. The effects of intrinsic torsional potentials, intramolecular hydrogen bonds, and librational entropy on relative conformational energies and locations of minima are discussed. The results are categorized most easily by use of a new conformational letter code that is introduced here.

Prediction of three-dimensional structures of enzyme-substrate and enzyme-inhibitor complexes of lysozyme.

Conformational energy calculations were used to predict the three-dimensional structures of enzyme-substrate and enzyme-inhibitor complexes of lysozyme. A global search method, involving the use of a disaccharide fragment molecule, was used initially to determine all favorable binding regions at the active site. It is shown that the binding of a series of (nonfragmented) oligomers of N-acetylglucosamine is highly specific. The results show further that (a) the enzyme recognizes only one backbone conformation of the oligomer, corresponding to a left-handed helix, and (b) for saccharides containing two or more N-acetylglucosamine residues, two residues bind preferentially to the C and D sites. The calculations also suggest that the chair form of N-acetylglucosamine can bind to the D region. The saccharide residues of tetra-N-acetylglucosamine bind to the A-B-C-D sites, with the residues at the A-B-C sites having essentially the same conformation and orientation as those in the x-ray structure of tetra-N-acetylglucosamine-delta-lactone bound to lysozyme.

Stability of cis, trans, and nonplanar peptide groups.

Conformational energy calculations using ECEPP (Empirical Conformational Energy Program for Peptides) were performed on the molecular fragment Calpha1C'ONHCalpha2, on N-methylacetamide, and on several peptide molecules including N-acetyl-N'-methylglycineamide (Gly single residue), N-acetyl-N',N'-dimethylglycine-amide, and N-acetyl-N'-methylamide dipeptides of Gly-Gly and Gly-Pro. Energy minimization was carried out with peptide groups taken in both the cis and trans conformations, and the librational entropy and conformational free energy were determined at each minimum. It was found that the instability of cis in Gly-Gly comes primarily from interactions of the Calpha1 and HCalpha1 atoms with the Calpha2 and HCalpha2 atoms, and also from avorable interactions present in the trans form which are disallowed in the cis form, and from conformational entropy. The instability of cis in Gly-Pro is much less than in Gly-Gly because unfavorable interactions of the type CalphaH-CalphaH present in the cis conformation of Gly-Gly are present in both the cis and trans forms of Gly-Pro. The instability of cis in Gly-Pro arises mainly from the change in electrostatic energy caused by the restricted rotation about the N-Calpha bond of Pro. Entropy accounts for about 0.5 kcal/mol of the instability of cis in Gly-Pro compared with about 1.5 kcal/mol in Gly-Gly. The calculated fraction (4%) of cis in Gly-pro is in good agreement with the experimental value (5%) for related peptides in nonpolar solvents. When the dihedral angle omega of the central peptide bond in these dipeptides is allowed to vary during energy minimization, the deviations from planarity are only 1-3 degrees in low-energy minima of Gly-Gly but as much as 10 degrees in Gly-Pro. A comparison of these results with calculations in which the peptide bond was held fixed in the planar trans conformation shows that conformation-dependent properties of blocked dipeptides can be represented adequately without allowing omega to vary.