The catalytic mechanism of endoplasmic reticulum signal peptidase appears to be distinct from most eubacterial signal peptidases

Many type I signal peptidases from eubacterial cells appear to contain a serine/lysine catalytic dyad. In contrast, our data show that the signal peptidase complex from the endoplasmic reticulum lacks an apparent catalytic lysine. Instead, a serine, histidine, and two aspartic acids are important for signal peptidase activity by the Sec11p subunit of the yeast signal peptidase complex. Amino acids critical to the eubacterial signal peptidases and Sec11p are, however, positioned similarly along their primary sequences, suggesting the presence of a common structural element(s) near the catalytic sites of these enzymes.

Waterbirths: regional audit of infection control practices

Waterbirths are increasingly being offered as an option, although concerns about associated infection risks have been expressed. We undertook an audit of current practice in our region to help formulate an infection control policy. Questionnaires were sent to the Infection Control Nurses at 16 centres, with a request for completion in conjunction with the Infection Control Doctor. Fourteen (88%) centres responded, 11 of which carried out waterbirthing. Eight had permanent on-site pools, of which five were permanently plumbed in and provided with separate water inlets and outlets. All eight centres had infection control policies for waterbirthing. Six policies included care of the pool using detergent and disinfectant (chlorine-releasing compounds) and two using detergent alone. In none of the centres were the mothers tested for blood-borne viruses. Six centres collected data on infection in mother or child, and two carried out regular microbiological testing of pools. Infection control policies for waterbirths should include instructions for pool maintenance and decontamination, for prevention of legionella, for universal precautions and for use of personal protective equipment. Post-natal surveillance of mothers and babies is required in order to ascertain infection rates.

Estimation of the caries-related risk associated with infant formulas

PURPOSE

Baby bottle tooth decay (BBTD) affects 6% of children under three years of age and is associated with inappropriate bottle use. The objective of this study was to estimate the caries-related risk associated with 26 infant formulas and whole milk.

METHODS

First, the plaque pH of adult volunteers was monitored before and after an oral rinse with infant formula to determine the minimum pH obtained in response to each formula. Second, Streptococcus sobrinus 6715 was cultured in each infant formula, and the increase in the number of colony forming units was measured. Third, each infant formula was incubated with powdered enamel and the solubility of enamel mineral was calculated in the absence of bacteria. Fourth, each formula was mixed with standardized concentrations of acid to determine the buffering capabilities. Finally, enamel windows were created on extracted permanent molars and exfoliated primary incisor crowns that were then colonized with mutans streptococci and incubated with infant formula. Caries was assessed visually and radiographically for 18 weeks. The length of time required for the development of enamel caries, dentinal caries and pulpal involvement was recorded.

RESULTS

One-way or two-way ANOVA of these five assays demonstrated that 1. Plaque pH varied in response to oral rinsing with infant formula and most formulas did have the ability to reduce the pH significantly below the pH obtained after rinsing with water 2. Some infant formulas supported significant bacterial growth 3. Enamel mineral was dissolved by incubation with certain infant formula 4. The buffer capacity varied among the infant formulas tested 5. The length of time required for caries to reach dentin or pulp differed for the formulas, with some formulas causing dentinal caries by 3.4 weeks and pulpal involvement by 7.2 weeks.

Nicardipine versus nitroprusside for controlled hypotension during spinal surgery in adolescents

Nicardipine or nitroprusside was used to induce controlled hypotension in healthy adolescents with idiopathic scoliosis undergoing spinal fusion. Twenty patients were randomly assigned to the nitroprusside (N) or nicardipine (C) group. All patients received a standardized anesthetic. A target mean arterial blood pressure (MAP) of 60 mm Hg was achieved by varying the vasoactive infusions only. Moderate hemodilution (PCV = 25) and intraoperative blood salvage were used in all cases. Hemodynamic variables, blood loss, occurrence of reflex tachycardia, and reversibility of the hypotensive state were compared between the two groups. Significant differences were observed between the two groups in the amount of blood loss and reversibility of the hypotensive state. Group C had less blood loss (761 +/- 199 mL) than Group N (1297.5 +/- 264, P < or = .05). Time to restoration of baseline MAP was longer with Group C (26.8 +/- 4.0 min) than Group N (7.3 +/- 1.1 min, P < or = 0.001). Both drugs rapidly achieved a stable, controlled hypotensive state and an acceptable operating field. There was no statistically significant difference between groups with respect to the amount of crystalloid administered or urine output. These results suggest that nicardipine is a safe, effective drug for controlled hypotension in this population and that it may offer the significant advantage of reduced blood loss in these patients.

In addition to SEC11, a newly identified gene, SPC3, is essential for signal peptidase activity in the yeast endoplasmic reticulum

Among the three characterized subunits comprising the signal peptidase complex of the yeast Saccharomyces cerevisiae (Sec11p, Spc1p, and Spc2p), only Sec11p is essential for cell growth, signal peptide cleavage, and signal peptidase-dependent protein degradation. Here we report the cloning of the SPC3 gene encoding the homolog to mammalian signal peptidase subunit SPC22/23. We find that Spc3p is also required for cell growth and signal peptidase activity within the yeast endoplasmic reticulum.

Absorption of radiocaesium by sheep after ingestion of contaminated soils

The absorption of 137Cs by sheep following ingestion of contaminated soil was studied using an established dual isotope method. Two agricultural soils were studied: an alluvial gley contaminated by discharges to the sea from the Sellafield Reprocessing Plant, and a lowland organic soil that had been artificially contaminated. Values of the true absorption coefficient of radiocaesium of 0.19 +/- 0.03 and 0.03 +/- 0.01, respectively, were obtained for these soils. This implies that availability of soil-associated radiocaesium for uptake following ingestion is up to about 20% of that when the activity is incorporated in vegetation. These results have been compared to estimates of availability made using an in-vitro approach described previously and found to be in good agreement. However, comparison with in-vitro data obtained for an upland peat indicated that absorption from some upland organic soils could be greater than from the lowland organic soil.

Structurally related Spc1p and Spc2p of yeast signal peptidase complex are functionally distinct

Two subunits of the mammalian signal peptidase complex, SPC12 and SPC25, share similar membrane topologies with the majority of each protein oriented toward the cytoplasm. Such similarities may suggest that these proteins perform redundant functions in signal peptidase activity. In the present study, we addressed this issue through analysis of the yeast homologs to SPC12 and SPC25, Spc1p and Spc2p. We show that both Spc1p and Spc2p are nonessential for signal peptidase activity and growth of yeast cells and that null mutations in the genes encoding Spc1p and Spc2p are synthetically lethal with a conditional mutation affecting Sec11p, an essential subunit of yeast signal peptidase. However, a high copy plasmid encoding Spc1p suppresses the conditional sec11 mutation, whereas the corresponding plasmid encoding Spc2p does not suppress sec11. Moreover, Spc2p, but not Spc1p, is important for signal peptidase activity and cell viability at high temperatures. These results indicate that although both Spc1p and Spc2p are noncatalytic, they are functionally distinct. Evidence is also presented that a double mutant lacking Spc1p and Spc2p grows well relative to wild type yeast cells, indicating that the signal peptidase complex missing at least two of its subunits is sufficient for signal peptidase activity in vivo.

The homologue of mammalian SPC12 is important for efficient signal peptidase activity in Saccharomyces cerevisiae

The multisubunit signal peptidase catalyzes the cleavage of signal peptides and the degradation of some membrane proteins within the endoplasmic reticulum (ER). The only subunit of this enzyme functionally examined to date, yeast Sec11p, is related to signal peptidase I from bacteria. Since bacterial signal peptidase is capable of processing both prokaryotic and eukaryotic signal sequences as a monomer, it is unclear why the analogous enzyme in the ER contains proteins unrelated to signal peptidase I. To address this issue, the gene encoding Spc1p, the yeast homologue to mammalian SPC12, is isolated from the yeast Saccharomyces cerevisiae. Spc1p co-purifies and genetically interacts with Sec11p, but unlike Sec11p, Spc1p is not required for cell growth or the proteolytic processing of tested proteins in yeast. This indicates that only a subset of the ER signal peptidase subunits is required for signal peptidase and protein degradation activities in vivo. Through both genetic and biochemical criteria, Spc1p appears, however, to be important for efficient signal peptidase activity.

Transfer of radionuclides to vegetable and other crops grown on land reclaimed from the sea

An area of reclaimed land on the Lancashire coast has been used to grow a wide range of crops to provide data on transfer parameters of radionuclides in foodchains when the activity is almost entirely of marine origin. Activity concentrations in the foodstuffs were low and not of radiological significance. However, meaningful results could be obtained if large sample sizes were employed. This paper sets out the methodology applied to a substantial field investigation of transfer to vegetable crops. The large sample sizes could be accommodated adequately with only minor modifications to established analytical procedures. The results of the study are discussed briefly. Since the growing conditions were virtually identical for each crop, comparisons of transfer factors between the different crops should therefore be valid. For some radionuclides, notably 239,240Pu, 241Am and 99Tc, the work has added significantly to the data that are presently available. For most of the radionuclides studied, uptake by crops could be adequately predicted using the parameter values currently used in generic assessments, but for 99Tc, lower values would be more appropriate.

Neutralising antibodies after streptokinase treatment for myocardial infarction: a persisting puzzle

OBJECTIVE

To determine the development of titres of streptokinase (SK) neutralising antibodies after a single dose of SK, to establish when titres decrease to levels at which a second dose might be effective.

DESIGN

Analyses of blood samples taken from patients at intervals after SK administration.

SETTING

Australian public hospital.

PATIENTS

104 patients with acute myocardial infarction who were treated with SK and 27 controls who were not.

OUTCOME MEASURE

SK neutralising antibodies were measured once in each of the 27 controls and on 166 occasions in the 104 treated patients.

RESULTS

Titres of SK neutralising antibodies rose after SK administration but returned to control levels by 2 years.

CONCLUSIONS

SK might be effective again as a thrombolytic agent as early as 2 years after a single dose. These results are at variance with most previously published data and the reasons for this are not clear. Data evaluating patency rates after standard doses of streptokinase in patients with increased titres of neutralising antibodies are necessary before re-exposure to streptokinase can be recommended.

A mutation affecting signal peptidase inhibits degradation of an abnormal membrane protein in Saccharomyces cerevisiae

Signal peptidase removes amino-terminal signal peptides from precursor proteins during or immediately following their translocation to the lumen of the endoplasmic reticulum (ER) and may participate in ER degradation, a poorly defined process whereby abnormal proteins are rapidly degraded early in the secretory pathway. Here, the involvement of signal peptidase in ER degradation is examined through the use of two chimeric membrane proteins that lack amino-terminal signal peptides: A189invHD, which contains sequences derived from arginine permease and histidinol dehydrogenase, and AHDK2, containing the ER-resident protein Kar2p fused to the carboxyl terminus of A189invHD. Degradation of approximately 95% of A189invHD is observed in yeast cells expressing enzymatically active signal peptidase, whereas only 60% undergoes rapid degradation in a sec11 mutant bearing a temperature-sensitive mutation in the gene encoding the 18-kDa subunit (Sec11p) of the signal peptidase complex. AHDK2 is proteolyzed in a reaction yielding at least two fragments in wild-type cells and in the sec11 mutant containing a plasmid bearing the SEC11 gene. The proteolytic reaction is catalyzed in a temperature-dependent manner in the sec11 mutant, with AHDK2 remaining stable at the nonpermissive temperature. Using conditional mutants defective in protein translocation into and out of the ER and in vitro protease protection studies, the site of degradation for AHDK2 is localized to the ER lumen. The data therefore indicate (i) A189invHD is degraded through both signal peptidase-dependent and independent processes; (ii) signal peptidase, specifically the Sec11p subunit, is required for the proteolysis of AHDK2; and (iii) the Kar2 fragment at the carboxyl terminus of AHDK2 permits detection of proteolytic intermediates.

Nonlethal sec71-1 and sec72-1 mutations eliminate proteins associated with the Sec63p-BiP complex from S. cerevisiae

The sec71-1 and sec72-1 mutations were identified by a genetic assay that monitored membrane protein integration into the endoplasmic reticulum (ER) membrane of the yeast Saccharomyces cerevisiae. The mutations inhibited integration of various chimeric membrane proteins and translocation of a subset of water soluble proteins. In this paper we show that SEC71 encodes the 31.5-kDa transmembrane glycoprotein (p31.5) and SEC72 encodes the 23-kDa protein (p23) of the Sec63p-BiP complex. SEC71 is therefore identical to SEC66 (HSS1), which was previously shown to encode p31.5. DNA sequence analyses reveal that sec71-1 cells contain a nonsense mutation that removes approximately two-thirds of the cytoplasmic C-terminal domain of p31.5. The sec72-1 mutation shifts the reading frame of the gene encoding p23. Unexpectedly, the sec71-1 mutant lacks p31.5 and p23. Neither mutation is lethal, although sec71-1 cells exhibit a growth defect at 37 degrees C. These results show that p31.5 and p23 are important for the trafficking of a subset of proteins to the ER membrane.

The occupational therapist as an expert analyst on the cost of future health care in legal cases

The purpose of this paper is to explain the legal criteria the court follows when awarding monies to an injured individual for Cost of Future Care. It also describes the role of, and procedures used by, the occupational therapist in analyzing future care costs for the court's consideration. It describes the benefits to the client, the legal system and society arising from the occupational therapist's expertise, and the role the therapist plays in obtaining information related to the client's case from other professionals.

Doing short term counseling: a six session model

1. Short term counseling in an occupational health setting is an effective means of reaching a population that may otherwise not have considered counseling. However, because of the time limits, the practitioner must be able to make a quick assessment of the kind of help needed. 2. The seven principles of short term treatment are: 1) mutual goal directedness; 2) quick problem identification; 3) reminder of finiteness of sessions; 4) making an appropriate referral; 5) confidentiality; 6) open communication; and 7) follow up. 3. In a six session model, sessions 1 and 2 are for assessment; sessions 3 and 4 are for development of insights and strategies; and sessions 5 and 6 are for termination. 4. Occupational health nurses with mental health training are ideal practitioners of short term counseling, because they can recognize many physical symptoms as having a psychological basis.

Isolation and mapping of human T-cell protein tyrosine phosphatase sequences: localization of genes and pseudogenes discriminated using fluorescence hybridization with genomic versus cDNA probes

This work reports the isolation, partial characterization, and chromosomal mapping of several human T-cell protein tyrosine phosphatase (PTPase) sequences and provides a direct comparison of the specificity of cDNA versus genomic probes in discriminating the location of genes versus pseudogenes by fluorescence in situ hybridization. In initial attempts to map the T-cell (TC) PTP gene using a 2-kb cDNA, several labeled sites were noted, raising the possibility of multiple related sequences within the genome. To address this, four genomic clones were obtained with homology to the TC PTP cDNA and characterized for their primary structure and their position within the human genome. Based on the presence or absence of an open reading frame and the intron/exon structure, two of these clones were found to be overlapping sequences encoding the true TC PTP gene and two were highly related but distinct processed pseudogenes. The TC PTP gene (gene symbol PTPN2) encoded by clones L17-2 and L5-1 localized to chromosome 18p11.2-p11.3, whereas pseudogenes encoded by clone L17-1, entitled TCPS1 (gene symbol PTPN2P1), and clone L18, entitled TCPS13 (gene symbol PTPN2P2), mapped to chromosomes 1q22-q24 and 13q12-q13, respectively. A direct comparison of the specificity of genomic and cDNA probes demonstrated that under identical conditions the genomic probes (containing both exon and intron sequences) readily identified a single specific site of hybridization, whereas the cDNA identified sites of both the gene and its pseudogenes. While providing mapping and sequencing information on the TC PTPase sequences, this work illustrates a strategy for addressing a recurrent problem in gene mapping studies where highly related sequences exist within the genome.

Prostate cancer--the impact of irradiation on urinary outlet obstruction

A series of 245 patients with prostate cancer treated by external irradiation was analysed to assess the impact of irradiation on urinary outlet obstruction. Prior to irradiation, obstruction was observed in 147/245 patients (60%). Irradiation either with or without hormonal therapy was as efficacious as transurethral resection of the prostate (TURP) in alleviating obstructive symptoms; 14/16 patients treated by irradiation alone responded, as did 19/19 who received hormonal therapy and irradiation and 109/112 who underwent TURP and irradiation. Following irradiation, 41/245 patients developed post-irradiation obstruction, 26/213 had post-irradiation strictures and 15/32 developed recurrent cancer. Surgical intervention was required less often for the management of recurrent obstruction caused by stricture as compared with recurrent cancer. TURP and urinary outlet obstruction acted as independent and additive variables to the development of post-irradiation stricture. Thus the avoidance of TURP in patients with obstructive symptoms reduced but did not eliminate the risk of developing a stricture.

Mutants in three novel complementation groups inhibit membrane protein insertion into and soluble protein translocation across the endoplasmic reticulum membrane of Saccharomyces cerevisiae

We have isolated mutants that inhibit membrane protein insertion into the ER membrane of Saccharomyces cerevisiae. The mutants were contained in three complementation groups, which we have named SEC70, SEC71, and SEC72. The mutants also inhibited the translocation of soluble proteins into the lumen of the ER, indicating that they pleiotropically affect protein transport across and insertion into the ER membrane. Surprisingly, the mutants inhibited the translocation and insertion of different proteins to drastically different degrees. We have also shown that mutations in SEC61 and SEC63, which were previously isolated as mutants inhibiting the translocation of soluble proteins, also affect the insertion of membrane proteins into the ER. Taken together our data indicate that the process of protein translocation across the ER membrane involves a much larger number of gene products than previously appreciated. Moreover, different translocation substrates appear to have different requirements for components of the cellular targeting and translocation apparatus.

C-terminal sequences can inhibit the insertion of membrane proteins into the endoplasmic reticulum of Saccharomyces cerevisiae

We have constructed three gene fusions that encode portions of a membrane protein, arginine permease, fused to a reporter domain, the cytoplasmic enzyme histidinol dehydrogenase (HD), located at the C-terminal end. These fusion proteins contain at least one of the internal signal sequences of arginine permease. When the fusion proteins were expressed in Saccharomyces cerevisiae and inserted into the endoplasmic reticulum (ER), two of the fusion proteins placed HD on the luminal side of the ER membrane, but only when a piece of DNA encoding a spacer protein segment was inserted into the fusion joint. The third fusion protein, with or without the spacer included, placed HD on the cytoplasmic side of the membrane. These results suggest that (i) sequences C-terminal to the internal signal sequence can inhibit membrane insertion and (ii) HD requires a preceding spacer segment to be translocated across the ER membrane.