Gene-gene effects on central processing of aversive stimuli

Emotional reactivity and regulation are fundamental to human behavior. As inter-individual behavioral variation is affected by a multitude of different genes, there is intense interest to investigate gene-gene effects. Functional sequence variation at two genes has been associated with response and resiliency to emotionally unpleasant stimuli. These genes are the catechol-O-methyltransferase gene (COMT Val158Met) and the regulatory region (5-HTTLPR) of the serotonin transporter gene. Recently, it has been proposed that 5-HTT expression is not only affected by the common S/L variant of 5-HTTLPR but also by an A to G substitution. Using functional magnetic resonance imaging, we assessed the effects of COMT Val(158)Met and both 5-HTT genotypes on brain activation by standardized affective visual stimuli (unpleasant, pleasant, and neutral) in 48 healthy subjects. Based on previous studies, the analysis of genotype effects was restricted to limbic brain areas. To determine allele-dose effects, the number of COMT Met158 alleles (i.e., lower activity of COMT) and the number of 5-HTT low expressing alleles (S and G) was correlated with the blood oxygen level-dependent (BOLD) response to pleasant or unpleasant stimuli compared to neutral stimuli. We observed an additive effect of COMT and both 5-HTT polymorphisms, accounting for 40% of the inter-individual variance in the averaged BOLD response of amygdala, hippocampal and limbic cortical regions elicited by unpleasant stimuli. Effects of 5-HTT and COMT genotypes did not affect brain processing of pleasant stimuli. These data indicate that functional brain imaging may be used to assess the interaction of multiple genes on the function of neuronal networks.

Two different Argonaute complexes are required for siRNA generation and heterochromatin assembly in fission yeast

The RNA-induced transcriptional silencing (RITS) complex, containing Ago1, Chp1, Tas3 and centromeric small interfering RNAs (siRNAs), is required for heterochromatic gene silencing at centromeres. Here, we identify a second fission yeast Argonaute complex (Argonaute siRNA chaperone, ARC), which contains, in addition to Ago1, two previously uncharacterized proteins, Arb1 and Arb2, both of which are required for histone H3 Lys9 (H3-K9) methylation, heterochromatin assembly and siRNA generation. Furthermore, whereas siRNAs in the RITS complex are mostly single-stranded, siRNAs associated with ARC are mostly double-stranded, indicating that Arb1 and Arb2 inhibit the release of the siRNA passenger strand from Ago1. Consistent with this observation, purified Arb1 inhibits the slicer activity of Ago1 in vitro, and purified catalytically inactive Ago1 contains only double-stranded siRNA. Finally, we show that slicer activity is required for the siRNA-dependent association of Ago1 with chromatin and for the spreading of histone H3-K9 methylation.

Tethering RITS to a nascent transcript initiates RNAi- and heterochromatin-dependent gene silencing

In the fission yeast Schizosaccharomyces pombe, the RNA-Induced Transcriptional Silencing (RITS) complex has been proposed to target the chromosome via siRNA-dependent base-pairing interactions to initiate heterochromatin formation. Here we show that tethering of the RITS subunit, Tas3, to the RNA transcript of the normally active ura4+ gene silences ura4+ expression. This silencing depends on a functional RNAi pathway, requires the heterochromatin proteins, Swi6/HP1, Clr4/Suv39h, and Sir2, and is accompanied by the generation of ura4+ siRNAs, histone H3-lysine 9 methylation, and Swi6 binding. Furthermore, the ability of the newly generated ura4+ siRNAs to silence a second ura4+ allele in trans is strongly inhibited by the conserved siRNA nuclease, Eri1. Surprisingly, silencing of tethered ura4+, or ura4+ inserted within centromeric heterochromatin, or some of the endogenous centromeric repeat promoters, is not associated with changes in RNA polymerase II occupancy. These findings support a model in which targeting of nascent transcripts by RITS mediates chromatin modifications and suggest that cotranscriptional processing events play a primary role in the silencing mechanism.

EJC-independent degradation of nonsense immunoglobulin-mu mRNA depends on 3' UTR length

Inconsistent with prevailing models for nonsense-mediated mRNA decay (NMD) in mammals, the mRNA levels of immunoglobulin-mu (Ig-mu) genes with premature termination codons (PTCs) in the penultimate exon are still reduced by NMD when the intron furthest downstream is deleted. As in yeast, this exon junction complex-independent NMD of Ig-mu mRNAs depends on the distance between the termination codon and the poly(A) tail and suggests an evolutionarily conserved mode of PTC recognition.

Transcriptional silencing of nonsense codon-containing immunoglobulin minigenes

Cells possess mechanisms to prevent synthesis of potentially deleterious truncated proteins caused by premature translation-termination codons (PTCs). Here, we show that PTCs can induce silencing of transcription of its cognate gene. We demonstrate for immunoglobulin (Ig)-mu minigenes expressed in HeLa cells that this transcriptional silencing is PTC specific and reversible by treatment of the cells with histone deacetylase inhibitors. Furthermore, PTC-containing Ig-mu minigenes are significantly more associated with K9-methylated histone H3 and less associated with acetylated H3 than the PTC-free Ig-mu minigene. This nonsense-mediated transcriptional gene silencing (NMTGS) is also observed with an Ig-gamma minigene, but not with several classic NMD reporter genes, suggesting that NMTGS might be specific for Ig genes. NMTGS represents a nonsense surveillance mechanism by which truncation of a gene's open reading frame (ORF) induces transcriptional silencing through chromatin remodeling. Remarkably, NMTGS is inhibited by overexpression of the putative siRNase 3'hExo, suggesting that siRNA-like molecules are involved in NMTGS.

Nonsense-associated alternative splicing of T-cell receptor beta genes: no evidence for frame dependence

Mutations that generate premature translation-termination codons (PTCs) often result in production of alternatively spliced mRNAs. While in many cases, the PTC-causing mutation was found to affect splicing directly by disrupting an exonic splicing enhancer, induction of alternative splicing of TCR-beta pre-mRNA has been reported to be specific for mutations that prematurely terminate the open reading frame. During testing of a cyto-nuclear feedback model that would have explained how cytoplasmic translation could influence nuclear splicing of TCR-beta transcripts, control experiments questioned the frame dependence of the nonsense-associated altered splicing (NAS) of TCR-beta pre-mRNA. A subsequent detailed analysis of alternatively spliced TCR-beta mRNA expressed from different minigene constructs with nonsense, silent, or frame-shift mutations at various positions revealed no correlation between truncation of the reading frame and production of alternatively spliced mRNA. Our study thus contradicts the previously reported PTC specificity of TCR-beta NAS and points out the need for systematically testing the PTC specificity in other cases where NAS has been observed.

Alternative splicing induced by nonsense mutations in the immunoglobulin mu VDJ exon is independent of truncation of the open reading frame

In addition to triggering nonsense-mediated mRNA decay (NMD), premature translation-termination codons (PTCs) frequently induce alternative splicing, an observation referred to as nonsense-associated alternative splicing (NAS). In many cases, NAS is induced because the nonsense mutation alters a splicing signal, such as inactivating an exonic splicing enhancer. However, for a few genes, NAS was reported to be PTC specific, implying that a translation signal could influence splicing. Here, we investigated whether production of a previously undetected alternatively spliced transcript from immunoglobulin mu (Ig-mu) depends on premature termination of the open reading frame. We show that PTCs at different positions in the VDJ exon of an Ig-mu minigene activate usage of an alternative 3' splice site, generating an alternative transcript that lacks the initial PTC and a previously identified NMD-promoting element (NPE), but contains new PTCs because of a frame shift. Corroborating the importance of the NPE for maximal NMD response, the alternative transcript is only moderately down-regulated by NMD. We further demonstrate that NAS of Ig-mu minigene transcripts is not PTC specific. This finding, together with our results that contradict the previously reported frame dependence of TCR-beta NAS, challenges the idea that cells might possess mechanisms that would allow regulation of splice site selection in response to premature termination of the ORF.

Das Aneurysma spurium der A.�genus superior lateralis

Arterial complications after total knee arthroplasty are rare. If the formation of a false aneurysm does occur, it usually affects the popliteal artery. We report the case of an 77 year old female with a false aneurysm of the lateral superior genicular artery. The patient was suffering from gonarthrosis and received a duocondylar knee replacement without resurfacing of the patella. Postoperatively, she reported anterior knee pain and a revision of the joint with lateral release was carried out. In the third postoperative week, a painful swelling in the lateral and superior aspect of the knee occurred. A scintigraphic investigation with enrichment in the early period was misinterpreted as infection. Ultrasonographic and angiographic investigations gave the right diagnosis of a false aneurysm. In the same angiographic investigation, the aneurysm could be cured by coil embolisation. The interval between the operation leading to the problem and the formation of the aneurysm, as well as the low incidence of this complication, made it hard to diagnose. Ultrasonographic and angiographic examinations allow for proper diagnosis in cases of unclear painful swellings. When dealing with an arterial complication following total knee arthroplasty, a specialized radiologist or vascular surgeon should be consulted immediately.

Efficient downregulation of immunoglobulin mu mRNA with premature translation-termination codons requires the 5'-half of the VDJ exon

Premature translation-termination codons (PTCs) elicit rapid degradation of the mRNA by a process called nonsense-mediated mRNA decay (NMD). NMD appears to be significantly more efficient for mRNAs of genes belonging to the immunoglobulin superfamily, which frequently acquire PTCs during VDJ rearrangment, than for mRNAs of other genes. To identify determinants for efficient NMD, we developed a minigene system derived from a mouse immunoglobulin micro gene (Ig-micro) and measured the effect of PTCs at different positions on the mRNA level. This revealed that PTCs located downstream of the V-D junction in the VDJ exon of Ig-micro minigenes and of endogenous Ig-micro genes elicit very strong mRNA downregulation, whereas NMD efficiency decreases gradually further upstream in the V segment where a PTC was inserted. Interestingly, two PTCs are in positions where they usually do not trigger NMD (<50 nt from the 3'-most 5' splice site) still resulted in reduced mRNA levels. Using a set of hybrid constructs comprised of Ig-micro and an inefficient substrate for NMD, we identified a 177 nt long element in the V segment that is necessary for efficient downregulation of PTC-containing hybrid transcripts. Moreover, deletion of this NMD-promoting element from the Ig-micro minigene results in loss of strong NMD.

Intranuclear degradation of nonsense codon-containing mRNA

Most vertebrate mRNAs with premature termination codons (PTCs) are specifically recognized and degraded by a process referred to as nonsense-mediated mRNA decay (NMD) while still associated with the nucleus. However, it is still a matter of debate whether PTCs can be identified by intranuclear scanning or only by ribosomes on the cytoplasmic side of the nuclear envelope. Here we show that inhibition of mRNA export by two independent approaches does not affect the downregulation of PTC-containing T-cell receptor beta transcripts in the nuclear fraction of mammalian cells, providing strong evidence for intranuclear NMD. Our results are fully consistent with recently reported evidence for nuclear translation and suggest that an important biological role for nuclear ribosomes is the early elimination of nonsense mRNA during a pioneer round of translation.

Osteoid osteoma: technique of computed tomography-controlled percutaneous resection using standard equipment available in most orthopaedic operating rooms

Symptoms of osteoid osteoma are cured by removing the nidus. 'En-bloc' resection is often not successful because the nidus is hard to find and remove totally. Recently, minimally invasive procedures have been advocated for the resection of osteoid osteoma. Preceding investigators have used a set of special instruments. The nidus is best localized with computed tomography (CT). Surgery under CT control is only possible with minimal invasive procedures. A technique using standard equipment usually available in the operating room can be used successfully for CT-guided removal of the nidus. We report our preliminary results with 17 patients (12 men, 5 women) with an average age of 22 years (range 6-57 years). All patients were pain-free immediately after the operation. The average follow-up was 8.4 months (range 1-22 months) and the average operating time 75 min (range 50-130 min). Ten patients could be treated as outpatients. The average time in hospital after surgery was 1.5 days (range 1-3 days). There were two complications, one superficial wound infection and one change of operative technique to an open procedure due to a technical problem. The diagnosis could be confirmed histologically.

The epidemiology of fractures of the distal femur

Between 1980 and 1989, reports on 2,165 fractures of the distal part of the femur (1,051 women and 1,114 men) were collected by AO Documentation and are analyzed in the present paper. The number of fractures showed a bimodal pattern with a marked variation in the number of fractures in relation to gender and age. A larger prevalence of fractures was observed either in young men (about 20 years old, traffic or sport) and in old women (about 70, fall at home, osteoporosis).

The epidemiology of fractures of the proximal femur

Between 1980 and 1989, reports on 21,145 fractures of the proximal part of the femur (15,428 women and 5,717 men) were collected by AO Documentation and are analysed in the present paper. The number of fractures increases exponentially with age for women and for men. Up to 50, the number of fractures is higher for men than for women and vice versa after 55 years. The exponential increase in the number of fractures with age appears for all the types A1 to B3 for both women and men. No special increase has been identified for women after 50 (expected age of menopause).

The epidemiology of diaphyseal fractures of the tibia

AO Documentation collected reports of nearly five thousand diaphyseal tibial fractures occurring in the 1980s. The following conclusions can be drawn: i. The number of fractures affecting men is twice that affecting women. ii. These fractures occurred mainly in younger people (under 40 years of age) and no increase occurred in elderly people. iii. Most bending fractures occurred in young men (20-30 yrs) and the torsion fractures affected men and women of about 40 equally. iv. The number of simple fractures (type A) is about the same as for fractures with one fragment (type B).

Novel dialysis cannulas: are they worth the higher price tag?

Accessory hemodialysis equipment, including dialysis cannulas, usually lack controlled and independent testing before being introduced onto the market. The aim of this study is a prospective comparison of a newly designed curved-tip dialysis cannula with a standard dialysis cannula of the same size from the same manufacturer. Fifteen chronic dialysis patients were enrolled onto a prospective 4-month crossover study. All patients had arteriovenous fistulas, except for two patients with polytetrafluoroethylene grafts. The routinely used standard cannulas were replaced by either a curved-tip 15G cannula or a new standard 15G cannula from the same manufacturer. The two cannulas were compared with respect to puncture-related pain and/or problems and bleeding complications, as well as blood-flow dynamics. Venous and arterial access pressures were recorded at blood-flow rates of 100 to 400 mL/min. Linear regression analyses of arterial and venous pressure profiles showed the same regression lines for the standard and curved-tip cannulas. Plasma haptoglobulin levels and occlusion times necessary to stop bleeding after removal of the cannulas did not differ between the two cannulas. Both patients and nurses independently reported equal puncture-related pain and/or problems for both cannulas on visual analogue scales. No correlation was found between puncture problems reported by nurses and puncture pain reported by patients. The curved-tip cannula does not offer an advantage compared with the less expensive standard cannula. Controlled testing of advertised advantages by manufacturers of accessory equipment should be a prerequisite before introduction into routine clinical treatment.

Longitudinal monthly body measurements from 1 to 12 months of age: a study by practitioners for practitioners. Zurich Association of Practicing Paediatricians

A longitudinal growth study with monthly measurements during the 1st year of life was conducted by nine paediatricians working in private practice in Zurich. Of 92 children, none was lost to the study and only 32 of 1104 planned visits were missed; the quality of the measurements was comparable to that of a specialised university clinic. Compared to the Zurich Longitudinal Growth Studies, children of this study were considerably heavier and taller. In 92% of the subjects, growth velocity was at least once outside the reference range (3rd 97th percentile). For weight increments, the corresponding proportion was 87%.

CONCLUSIONS

The data indicate that current standards for the 1st year of life for the Zurich area might no longer be appropriate and need to be updated. The currently used velocity percentiles based on 3-monthly measurements are not suitable to assess individual height and weight increments calculated from monthly measurements.

Transjugular intrahepatic portosystemic shunting (TIPS) with balloon-expandable and self-expanding stents: technical and clinical aspects after 3 1/2 years' experience

PURPOSE

To evaluate prospectively our experience with transjugular intrahepatic portosystemic shunt (TIPS) using four different metallic stents.

METHODS

Between November 1991 and April 1995, 57 patients (41 men and 16 women; age 35-72 years, mean 54 years) underwent the TIPS procedure. Techniques for portal vein localization before and during TIPS were fluoroscopy, computed tomography (CT) studies, wedged hepatic venography, arterial portography, and ultrasound. After predilation we deployed balloon-expandable (n = 48) and self-expanding (n = 45) metallic stents. Fifteen patients underwent variceal embolization. Initial follow-up angiograms (mean 6.9 months, range 3-24 months) were obtained in 39 of these patients.

RESULTS

Fifty-three patients (93%) had successful TIPS placement. The mean decrease in portal pressure was 42.7%. Besides fluoroscopy, the most helpful techniques for portal vein localization were venography and CT. Residual stenosis (n = 1) and late shortening (n = 4) of Wallstents resulted in shunt dysfunction. The technical problems encountered with the Palmaz stent resulted from its lack of flexibility. We combined balloon-expandable and self-expanding stents in 12 patients. The 30-day and late follow-up (mean 11.9 months) percutaneous reintervention rates were 11.3% and 64.2%, respectively. There were no clinically significant complications related to the TIPS insertions.

CONCLUSION

An ideal stent does not exist for TIPS, and the authors recommend combining a Palmaz stent with a flexible self-expanding stent.

Mechanism of the antiischemic effect of mibefradil, a selective T calcium channel blocker in dogs: comparison with amlodipine

Calcium channel blockers are active in variant angina principally by preventing coronary vasospasm. However, a direct antiischemic effect may also occur. In open-chest dogs, an attack of variant angina was mimicked by a 2-min critical coronary stenosis, and the following reversible myocardial ischemia was assessed by measuring the decrease of segmental shortening. We compared the antiischemic mechanism of mibefradil, a T and L calcium channel blocker, with that of amlodipine, a pure L channel blocker. Both drugs showed a similar relationship between the decrease of the rate-pressure product and the antiischemic effect, but only mibefradil reduced heart rate. Amlodipine and mibefradil at the highest doses tested (20 and 70 micrograms/kg/min, respectively) restored 68 +/- 8 and 76 +/- 5% of segmental shortening in the ischemic area, respectively, as compared with preischemic values. Matching blood pressure (by intraaortic balloon) or heart rate (by atrial pacing) to predrug values showed that the antiischemic effect was mainly afterload-dependent for amlodipine and heart rate-dependent for mibefradil. We conclude that in variant angina, in addition to their antivasospastic effects, calcium channel blockers may be antiischemic by a direct myocardial effect associated with a decrease of the rate pressure product. Blockade of the T channel does not seem to participate in the direct antiischemic effect of mibefradil but could explain the decrease of heart rate.

[Simultaneous measumrement of the renal excretion of 131I-hippuran and 99mTc-MAG3]

This study describes methods of measuring simultaneously the renal excretion of two radiopharmaceuticals and of evaluating their different kinetics. For quantification of the dynamic contributions of scattered radiation in a double-radionuclide study a high-resolution pure germanium detector was used. The geometry of the arrangement was a semi-shielded whole-body counter according to E. Oberhausen. An intra-individual comparison of the renal elimination of 99mTc-MAG3 and 131I-Hippuran shows a systemic difference between both tracers depending on the time after injection, its average being around 11% between the 10th and 20th min. The inter-individual comparison shows deviations from the mean between -29 and +20%.

[Clinical results with the limited contact DCP plate of titanium--a prospective study of 504 cases]

From the beginning of 1988 to July 1991, ten Swiss and German clinics undertook to document all cases of internal fixation using the titanium LC-DCP as part of a prospective multicenter study. The follow-up period was 14.2 months on average. The clinical results of 504 fixations were convincing. The follow-up rate was 72%. Of these, 95% healed without complication. The most frequent complication was delayed healing which occurred in 2.5% of cases. The infection rate was low (1.1%). A separate comparison of DCP fixations on the tibial shaft in 1984-1988 demonstrated the obvious biological compatibility of the new plate and shows that excellent results can be obtained using plate fixation.

Simultane Messung der renalen Ausscheidung von 131J-Hippuran und 99mTc-MAG3

In der vorliegenden Arbeit werden methodische Ansätze für einen simultanen Vergleich zweier nierengängiger Radiopharmaka dargestellt. Zur Quantifizierung der bei Doppelisotopenuntersuchungen auftretenden dynamischen Streuanteile wurde ein hochauflösender Reinst-Germanium-Detektor eingesetzt. Die Meßgeometrie entsprach der von Oberhausen beschriebenen Methode des teilabgeschirmten Ganzkörperzählers. Damit wurde erstmals ein Vergleich von MAG3 mit Hippuran durchgeführt, der 1. unter idealen meßtechnischen Bedingungen erfolgte und 2. bei simultaner Anwendung der Radiodiagnostika mögliche biologische Schwankungen bei der renalen Elimination ausschloß. Ein intraindividueller Vergleich der renalen Elimination von 99mTc-IVIAG3 und 131J-Hippuran läßt zeitabhängige systematische Differenzen zwischen beiden Tracern erkennen, die zwischen der ca. 10. und 20. Minute nach Untersuchungsbeginn im Mittel etwa 11% betrugen. Ein interindividueller Vergleich hingegen zeigte im Extrem Abweichungen vom Mittelwert zwischen -29 und +20%.

Documentation

In the period from 1. January to 31. December 1992, the new pinless external fixator was applied in eight European and North American clinics as part of a prospective multicentric study run by the AO/ASIF Documentation Centre. The aim of this study was to determine the indications, handling, and clinical results with the new fixator. The new pinless fixator was used 77 times on a total of 75 patients. The main indications were fresh tibial shaft fractures for which immediate definitive treatment was impossible. The majority of cases were secondarily stabilized with an unreamed tibial nail once the local and/or general condition of the patient had improved. In the remaining cases the pinless fixator was used for calcaneal and tibial head traction, segment transport and temporary stabilization in cases of tibial infection. Only after long-term application of the fixator was local infection at the pin site observed. There were no other complications. The new pinless fixator is a valuable addition in the treatment of fresh tibial fractures, in particular, in those cases which cannot be primarily treated due to contributing factors whether local or general.

[Classification of proximal femoral fractures]

Based on the AO Classification of Fractures, the classification of fractures of the proximal femur will be explained. Especially the sub- and pertrochanteric fractures, as well as the fractures of the femoral neck will be considered. During the period from 1980-1989 26,126 fractures of the proximal femur were documented in the AO/ASIF Documentation Center. These fractures will be discussed regarding following aspects: dispersion of age and fractures, pre-existing systemic illnesses, general and local postoperative complications, choice of implant.

[The decentralized documentation system '90' of the Study Group for Osteosynthesis Problems (AO)]

The new decentralized documentation system '90' of the "Arbeitsgemeinschaft für Osteosynthesefragen" (Association for the Study of Internal Fixation to ASIF) will be introduced. This system is used for gathering clinical data of operatively treated fractures and their clinical outcome.

[Soft tissue infection--osteitis--osteomyelitis]

Statistically the posttraumatic osteitis shows a clear tendency to decrease from 1972-76 in comparison with 1982-86 (AO/ASIF-documentation). The incidence of infection varies considerably according to the different anatomical location of fractures. More recently atypical manifestations became of more importance and ask for differentiated bacteriological examinations. A close postoperative follow-up and exact wound-observations enable an immediate and adequate therapy in case of an infection.

[Nosocomial infections in a university hospital. Results of a prospective study of infections in a medical and surgical ward and a surgical intensive care unit]

The results of an 11-month pilot study of surveillance of nosocomial infections are reported. Prospective surveillance was performed by daily examination of the microbiology reports and daily visits by the infection control nurse to the ward for the review of charts and Kardex of all patients for detection of "infection clues". Work sheets were used to collect all data during the daily rounds. Infection rates were calculated by dividing the the total number of hospital-acquired infections by the total number of discharges during the surveillance period. Active surveillance was performed for 6 months in the surgical intensive care unit (SCIU), 5 months in the surgical ward (SW) and 9 months in the medical ward (MW). Of 1527 patients discharged from these wards, nosocomial infections developed in 158 patients (10.4%). The overall infection rate was 14% (214 nosocomial infections). The infection rate varied greatly from ward to ward due to different patient populations, invasive procedures and severity of underlying diseases. Incidence infection rates were 42.5% for the SICU, 19.6% for the SW and 4.1% for the MW. The major sites affected were surgical wounds (42%), urinary tract (23%), respiratory tract (19%) and bloodstream (8%). The major etiologic agents associated with these nosocomial infections were E. coli, Pseudomonas aeruginosa, enterococci and Staphylococcus aureus. Conclusions drawn from the results of surveillance are discussed. The major benefits of an effective surveillance program for nosocomial infections are (a) estimates of the endemic levels of nosocomial infection, (b) identification of the nosocomial pathogens commonly encountered within a given institution, (c) identification of risk factors and (d) prompt recognition of epidemics. These data provide the necessary basis for an effective infection control program.

On the kinetics and mechanism of enoate reductase

Enoate reductases from Clostridium spec. La 1 and Clostridium kluyveri show a rather broad substrate specificity i.e. many alpha,beta-unsaturated carboxylates are reduced in a NADH-dependent reaction. The relative rates for different substrates are different for both reductases. The Km value of NADH for the reductase from C. spec. La 1 is about 12 muM. The transhydrogenase activity (reduction of N-acetylpyridine adenine dinucleotide) with NADH shows a maximum at pH 8 which is about 2 units higher than that for the reduction of enoates. Results of initial rate studies can be best explained by a Bi Bi ping pong mechanism. No back reaction and no proton exchange from 2(-3)H-labelled acylates could be demonstrated. NAD+ is a mixed-type inhibitor. The product inhibition constant Ki = 0.84mM and the dissociation constant for the dead-end inhibition complex 4.8mM. Aliphatic acylates show no measurable inhibition when they are applied in concentrations at the 100-fold Km values of the corresponding enoates. Measurable inhibitions can be observed with phenyl group-containing acylates. 3-Phenylpropionate (38mM) shows about 86% inhibition. Fumarate which is not a substrate inhibits the reduction of enoates by NADH as well as by reduced methylviologen. However, the reduction of NAD+ by reduced methylviologen as well that of acetylpyridine adenine dinucleotide by NADH is not inhibited by fumarate. On the other hand inhibitors such as morin or dicoumarol which probably bind to the flavin domain do not impair the reduction of enoates by reduced methylviologen however, all reductions with NADH are inhibited. These results are indicative for three binding domains: one for NADH which can be blocked by dicoumarol or morin, another for enoates which can be occupied by fumarate and a third one for reduced methylviologen. Enoate reductase splits off exclusively the (4S)-hydrogen atom from NADH. There is no direct hydrogen transfer from NADH to the products. Depending on the substrate concentration the isotope effect of the reduction of (E)-2-methyl-2-butenoate with (4S)-[4(-3)H]NADH varies from 6.8 to 1.3. The presence of NAD+ decreases the isotope effect.

Rhein as an electron acceptor for various flavoproteins and for electron transport particles

Rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) which has been previously employed as an inhibitor for electron transport particles, NADH dehydrogenase, and other flavoproteins is reducible under physiological conditions. Soluble hydrogenase from Alcaligenes eutrophus H 16, several flavoproteins, and electron transport particles from baker's yeast and from beef heart were found to catalyse NADH oxidation with 9 micrometers to 2mM rhein as the electron acceptor. Dithionite or enzymatically reduced rhein (lambda max = 408 nm) is immediately reoxidized to rhein lambda max = 437 nm) by oxygen. Cyclovoltagrams reveal the midpoint redox potentials --0.240 V, -0.270 V, -0.280 V, -0.335 V at pH 6.0, 7.0, 7.7, 9.2, respectively. Due to its redox behaviour, caution should be exercised using rhein as a flavin-site-directed inhibitor for biological electron transfer systems.

[Quantitative whole-body bone scintigraphy. II. Pharmacokinetics of osteotropic radiopharmaceuticals (author's transl)]

85Sr, 99mTc-Sn-pyrophosphate and 99mTc-Sn-methylene-diphosphonate, the most important agents for skeletal imaging, are compared with each other by calculation of the plasma clearance and the urinary excretion and by a series of quantitative whole-body scans. 85Sr the distribution volume in equilibrium is the largest, shifting of activity is demonstrable for several days after injection. 99mTc-Sn-MDP is excreted most quickly, equilibrium is reached early. There is no significant difference in skeletal uptake between the phosphate complexes. The distribution however is different: 85Sr is localized to a greater extent in the extremities, the phosphate complexes more in the trunk, 99mTc-Sn-MDP and 85Sr nearer the joints than 99mTc-Sn-pyrophosphate.