Occupational exposures to blood in a dental teaching environment: results of a ten-year surveillance study.

Evaluation of occupational exposures can assist with practice modifications, redesign of equipment, and targeted educational efforts. The data presented in this report has been collected as part of a ten-year surveillance program of occupational exposures to blood or other potentially infectious materials in a large dental teaching institution. From 1987 to 1997, a total of 504 percutaneous/non-intact skin and mucous membrane exposures were documented. Of these, 494 (98 percent) were percutaneous, and 10 (2 percent) were mucosal, each involving a splash to the eye of the dental care worker (DCW). Among the 504 exposures, 414 (82.1 percent) occurred among dental students, 60 (11.9 percent) among staff, and 30 (6 percent) among faculty. One hundred ninety-one (37.9 percent) exposures were superficial (no bleeding), 260 (51.6 percent) were moderate (some bleeding), and 53 (10.5 percent) were deep (heavy bleeding). Regarding the circumstances of exposure, 279 (54.5 percent) of the injuries occurred post-operatively (after the use of the device), and most were related to instrument clean-up; 210 (41.0 percent) occurred intra-operatively (during the use of the device); and 23 (4.5 percent) occurred when a DCW collided with a sharp object in the dental operatory (eight cases involved more than one circumstance). The overall exposure rate for the college was 2.46+/-0.11 SD per 10,000 patient visits. The average rate for the student population was 4.02+/-0.20 SD per 100 person-years, with the highest rates being observed among junior year students. The observed rates of occupational exposures to blood and body fluids in this report are consistent with published reports from several other educational settings. Dental teaching institutions are faced with the unique challenge of protecting the student and patient populations against bloodborne infections. Educational efforts must go beyond mere teaching of universal precautions and should include the introduction of safer products and clinical procedures that can minimize the risks associated with the hands-on aspects of the students' learning process.

Mortality among workers in a die-casting and electroplating plant.

A proportional mortality and case-referent analysis of 238 deaths among hourly employees in an automobile hardware manufacturing plant was conducted. The major operations of the plant were zinc die casting and electroplating. Chemical exposure included die-casting emissions and mists from chrome and nickel plating. The chief proportional mortality finding was a significant excess of lung cancer among both white men and women. A case-referent analysis indicated a possible association between lung cancer and work in certain departments. The findings support the hypothesis of a work-related carcinogenic risk. Follow-up recommendations have been made.

Conformational energy studies of oxytocin and its cyclic moiety.

Conformational energies were calculated for oxytocin in water, starting with a conformation proposed from nuclear magnetic resonance measurements in [U-(2)H](CH(3))(2)SO. Calculations on the isolated ring showed that conformations with one transannular hydrogen bond had the same energies as those without such bonds; those with two such hydrogen bonds do not appear to form. Calculations on the whole molecule also indicated the existence of several low-energy minima in the energy surface, and no preference for hydrogen-bond formation in the cyclic moiety; the hydrogen bond proposed between the Gly peptide NH and the Cys-6 C=O in the acyclic moiety can form. The proposed proximity of the tail to the ring is one of two low-energy conformations found. The Tyr side chain had two conformations of comparable energy, one over the ring between the Gln and Asn side chains, and the other with the Tyr side chain away from the ring. The oxytocin molecule appears to be flexible, and is probably sensitive to changes in its environment.

Evolution of neurophysin proteins: the partial sequence of bovine neurophysin-I (vasopressin-oxytocin-carrier proteins-automated amino-acid-sequence analysis-homology-protein evolution).

The sequence of the first 50 amino-acid residues of bovine neurophysin-I was determined. A comparison of this sequence with that of the 97-residue bovine neurophysin-II and the 92-residue porcine neurophysin-I molecules reveals a high degree of homology among these proteins. It is suggested that the binding site of neurophysin proteins for neurohypophyseal hormones is located in the middle portion of these molecules, where their sequences are virtually identical. The sequence data, as well as the occurrence of at least two neurophysins in both the pig and the cow, suggest that each species inherited at least two structural genes controlling the synthesis of these proteins. The most striking finding in the study was the observation of internal sequence homologies within the neurophysins. This result implies that these molecules arose by way of a series of partial gene duplications of a primitive gene that coded for a smaller ancestral protein.

Helix probability profiles of denatured proteins and their correlation with native structures.

The Zimm-Bragg formulation for the one-dimensional Ising model is applied to denatured proteins in order to compute helix probability profiles with different sigma and s parameters for the various amino acids; the latter are in principle determinable from melting curves for helix-coil transitions in random copolymers of amino acids. Using a tentative assignment of sigma and s values, we found a correlation for the propensity of a residue to be helical in the denatured protein and its occurrence in a helical region in the globular structure of the corresponding native protein. Thus, these incipient helical regions in the denatured chain may serve to nucleate the folding to form the native protein. Short-range interactions appear to determine the tendency for a residue to be helical or not, whereas long-range interactions may serve to carry out the nucleation and refolding processes.

The influence of short-range interactions on protein conformation. 3. Dipeptide distributions in proteins of known sequence and structure.

A statistical analysis is made of the distribution into alpha-helical and non-alpha-helical regions of the various dipeptide types appearing in a sample of seven proteins of known sequence and structure. By considering as a group all dipeptide types occurring at a given location relative to the reported helix-coil boundaries and examining the percentage of cases in which these appear in non-alpha-helical regions throughout the protein sample, we find a sharp change in the nature of the observed dipeptide types when the helix-coil boundary is crossed. Furthermore, we find that dipeptide types which occur in the coil region near the C-terminal end of helical segments are non-alpha-helical in almost 90 per cent of the cases in which they appear throughout the sample. No similar effect is found in the coil region near the N-terminal end of helical segments. These results give evidence for the importance of short-range interactions in determining protein conformation. They are also consistent with predictions based on a model for helix formation given in the second paper of this series.(1)

The influence of short-range interactions on protein onformation. II. A model for predicting the alpha-helical regions of proteins.

On the basis of earlier energy computations, the various single peptide units in proteins were designated as helix-making or helix-breaking.(1) With the use of these designations, empirical rules for distinguishing between alpha-helical and non-alpha-helical regions of proteins have been formulated. These rules include conditions for initiation and termination of a helical segment which, when combined with changes in the designation of three peptide units, correctly identify the helical or nonhelical character of over three fourths of the individual peptide units in four proteins of known amino acid sequence and structure: myoglobin, lysozyme, tosyl-alpha-chymotrypsin, and ribonuclease-A. The model is discussed, some of its predictions are checked, and further predictions about the structure of various proteins are made.