Identification of coenzyme M biosynthetic 2-phosphosulfolactate phosphatase. A member of a new class of Mg(2+)-dependent acid phosphatases

Coenzyme M (CoM; 2-mercaptoethanesulfonic acid) is the terminal methyl carrier in methanogenesis. Methanogenic archaea begin the production of this essential cofactor by sulfonating phosphoenolpyruvate to form 2-phospho-3-sulfolactate. After dephosphorylation, this precursor is oxidized, decarboxylated and then reductively thiolated to form CoM. A thermostable phosphosulfolactate phosphohydrolase (EC 3.1.3.-) catalyzing the second step in CoM biosynthesis, was identified in the hyperthermophilic euryarchaeon Methanococcus jannaschii. The predicted ORF MJ1140 in the genome of M. jannaschii encodes ComB, a Mg2+-dependent acid phosphatase that is specific for 2-hydroxycarboxylic acid phosphate esters. Recombinantly expressed purified ComB efficiently hydrolyzes rac-2-phosphosulfolactate, (S)-2-phospholactate, phosphoglycolate and both enantiomers of 2-phosphomalate. In contrast to previously studied phosphoglycolate phosphatases, ComB has a low pH optimum for activity, a narrow substrate specificity and an amino acid sequence dissimilar to any biochemically characterized protein. Like other phosphatases that function via covalent phosphoenzyme intermediates, ComB can catalyze a transphosphorylation reaction. Homologs of comB are identified in all available cyanobacterial genome sequences and in genomes from phylogenetically diverse bacteria and archaea; most of these organisms lack homologs of other CoM biosynthetic genes. The broad and disparate distribution of comB homologs suggests that the gene has been recruited frequently into new metabolic pathways.

Biosynthesis of the phosphodiester bond in coenzyme F(420) in the methanoarchaea

The biochemical route for the formation of the phosphodiester bond in coenzyme F(420), one of the methanogenic coenzymes, has been established in the methanoarchaea Methanosarcina thermophila and Methanococcus jannaschii. The first step in the formation of this portion of the F(420) structure is the GTP-dependent phosphorylation of L-lactate to 2-phospho-L-lactate and GDP. The 2-phospho-L-lactate represents a new natural product that was chemically identified in Methanobacterium thermoautotrophicum, M. thermophila, and Mc. jannaschii. Incubation of cell extracts of both M. thermophila and Mc. jannaschii with [hydroxy-(18)O, carboxyl-(18)O(2)]lactate and GTP produced 2-phospho-L-lactate with the same (18)O distribution as found in both the starting lactate and the lactate recovered from the incubation. These results indicate that the carboxyl oxygens are not involved in the phosphorylation reaction. Incubation of Sephadex G-25 purified cell extracts of M. thermophila or Mc. jannaschii with 7,8-didemethyl-8-hydroxy-5-deazariboflavin (Fo), 2-phospho-L-lactate, and GTP or ATP lead to the formation of F(420)-0 (F(420) with no glutamic acids). This transformation was shown to involve two steps: (i) the GTP- or ATP-dependent activation of 2-phospho-L-lactate to either lactyl(2)diphospho-(5')guanosine (LPPG) or lactyl(2)diphospho-(5')adenosine (LPPA) and (ii) the reaction of the resulting LPPG or LPPA with Fo to form F(420)-0 with release of GMP or AMP. Attempts to identify LPPG or LPPA intermediates by incubation of cell extracts with L-[U-(14)C]lactate, [U-(14)C]2-phospho-L-lactate, or [8-(3)H]GTP were not successful owing to the instability of these compounds toward hydrolysis. Synthetically prepared LPPG and LPPA had half-lives of 10 min at 50 degrees C (at pH 7.0) and decomposed into GMP or AMP and 2-phospho-L-lactate via cyclic 2-phospho-L-lactate. No evidence for the functioning of the cyclic 2-phospho-L-lactate in the in vitro biosynthesis could be demonstrated. Incubation of cell extracts of M. thermophila or Mc. jannaschii with either LPPG or LPPA and Fo generated F(420)-0. In summary, this study demonstrates that the formation of the phosphodiester bond in coenzyme F(420) follows a reaction scheme like that found in one of the steps of the DNA ligase reaction and in the biosynthesis of coenzyme B(12) and phospholipids.

Anticoagulation in the elderly

Oral anticoagulation therapy has demonstrated benefit in the treatment and prevention of a variety of thromboembolic disorders. Most individuals who receive oral anticoagulant therapy are elderly patients with nonvalvular atrial fibrillation and acute or recurrent venous thromboembolism. Anticoagulation in elderly patients poses unique challenges for the practicing clinician because they are simultaneously at higher risk for recurrent thromboembolism and major bleeding, including catastrophic intracranial hemorrhage. The pharmacology of warfarin in the elderly is reviewed, including important drug interactions and current dosing recommendations for elderly patients. Evidence of the benefits and risks of oral anticoagulation therapy are reviewed for patients with atrial fibrillation and venous thromboembolism. This information should enable practitioners to better assess the relative risks and benefit of oral anticoagulation therapy to guide treatment decisions in the elderly.

Methanococcus jannaschii generates L-proline by cyclization of L-ornithine

Cell extracts of Methanococcus jannaschii have been shown to readily convert L-ornithine to L-proline. This cyclization reaction proceeds with the loss of only the C-2 nitrogen, as has been documented for ornithine cyclodeaminase (EC 4.3.1.12). Since no gene homologous to that coding for ornithine cyclodeaminase is present in the genome of M. jannaschii, these results indicate that proline biosynthesis in M. jannaschii is accomplished by a previously unrecognized enzyme.

The first examples of (S)-2-hydroxyacid dehydrogenases catalyzing the transfer of the pro-4S hydrogen of NADH are found in the archaea

Reduction of 2-oxoacids to the corresponding (S)-2-hydroxyacids is an important transformation in biochemistry. To date all (S)-2-hydroxyacid dehydrogenases belonging to the L-lactate/L-malate dehydrogenase family have been found to transfer the pro-4R hydrogen of either NADH or NADPH to C-2 of the 2-oxoacid substrates during their reduction. Here, we report that recombinantly generated (S)-2-hydroxyacid dehydrogenases present in the methanoarchaea Methanococcus jannaschii and Methanothermus fervidus use the pro-4S hydrogen of NADH to reduce a series of 2-oxoacids to the corresponding (S)-2-hydroxyacids. This information as well as the low sequence identity between these archaeal enzymes and the L-lactate/L-malate family of enzymes indicate that these enzymes are not evolutionary related and therefore constitute a new class of (S)-2-hydroxyacid dehydrogenases.

Use of lepirudin in patients with heparin-induced thrombocytopenia and renal failure requiring hemodialysis

OBJECTIVE

To report two cases of successful lepirudin use in two patients with heparin-induced thrombocytopenia (HIT) and renal failure.

CASE SUMMARY

Two patients with renal failure requiring hemodialysis developed HIT syndrome during intravenous heparin therapy. Anticoagulation was necessary to prevent recurrent, acute venous thrombosis in one patient and to prevent arterial thrombosis associated with the use of an intraaortic balloon pump in the second. Intravenous lepirudin was initiated at doses of 0.01 mg/kg/h and 0.005 mg/kg/h, respectively, and titrated based on the activated partial thromboplastin time (aPTT). Steady-state doses were 0.015 mg/kg/h to maintain aPTT values of approximately 60 seconds in one patient, and 0.005-0.008 mg/kg/h to achieve an aPTT of approximately 45 seconds in the other patient.

DISCUSSION

Lepirudin is one of few anticoagulants that can be safely used in patients with HIT. Because it is eliminated through the kidneys, great care must be taken when administering lepirudin to patients with renal failure; in fact, its use is currently not recommended in patients requiring hemodialysis. Lepirudin effectively prevented acute thrombosis in both of our patients with documented HIT, with no bleeding complications. We describe how we selected the initial doses and report results of aPTT monitoring.

CONCLUSIONS

In patients with renal failure who develop HIT, lepirudin is one available alternative to heparin despite its poor renal elimination pattern and subsequently prolonged half-life.

Biosynthesis of the methanogenic cofactors

Our current knowledge of the pathways and genes involved in the biosynthesis of the methanogenic coenzymes methanopterin, coenzyme B, methanofuran, coenzyme F420, and coenzyme M is presented. Proposed reaction mechanisms for several of the novel reactions involved in the pathways are presented.

Warfarin therapy for an octogenarian who has atrial fibrillation

In North America, atrial fibrillation is associated with at least 75 000 ischemic strokes each year. Most of these strokes occur in patients older than 75 years of age. The high incidence of stroke in very elderly persons reflects the increasing prevalence of atrial fibrillation that occurs with advanced age, the high incidence of stroke in elderly patients, and the failure of physicians to prescribe antithrombotic therapy in most of these patients. This failure is related to the increased risk for major hemorrhage with advanced age, obfuscating the decision to institute stroke prophylaxis with antithrombotic therapy. This case-based review describes the risk and benefits of prescribing antithrombotic therapy for a hypothetical 80-year-old man who has atrial fibrillation and hypertension, and it offers practical advice on managing warfarin therapy. After concluding that the benefits of warfarin outweigh its risks in this patient, we describe how to initiate warfarin therapy cautiously and how to monitor and dose the drug. We then review five recent randomized, controlled trials that document the increased risk for stroke when an international normalized ratio (INR) of less than 2.0 is targeted among patients with atrial fibrillation. Next, we make the case that cardioversion is not needed for this asymptomatic patient with chronic atrial fibrillation. Instead, we choose to leave the patient in atrial fibrillation and to control his ventricular rate with atenolol. Later, when the INR increases to 4.9, we advocate withholding one dose of warfarin and repeating the INR test. Finally, when the patient develops dental pain, we review the analgesic agents that are safe to take with warfarin and explain why warfarin therapy does not have to be interrupted during a subsequent dental extraction.

Predictors of rehospitalization for symptomatic venous thromboembolism after total hip arthroplasty

BACKGROUND

Recent studies have shown that symptomatic venous thromboembolism after total hip arthroplasty most commonly develops after the patient is discharged from the hospital. Risk factors associated with these symptomatic thromboembolic events are not well defined.

METHODS

Using administrative data from the California Medicare records for 1993 through 1996, we identified 297 patients 65 years of age or older who were rehospitalized for thromboembolism within three months after total hip arthroplasty. We compared demographic, surgical, and medical variables potentially associated with the development of thromboembolism in these patients and 592 unmatched controls.

RESULTS

A total of 89.6 percent of patients with thromboembolism and 93.8 percent of control patients were treated with pneumatic compression, warfarin, enoxaparin, or unfractionated heparin, alone or in combination. In addition, 22.2 percent and 29.7 percent, respectively, received warfarin after discharge. A body-mass index (the weight in kilograms divided by the square of the height in meters) of 25 or greater was associated with rehospitalization for thromboembolism, with an odds ratio of 2.5 (95 percent confidence interval, 1.8 to 3.4). In a multivariate model, the only prophylactic regimens associated with a reduced risk of thromboembolism were pneumatic compression in patients with body-mass indexes of less than 25 (odds ratio, 0.3; 95 percent confidence interval, 0.2 to 0.6) and warfarin treatment after discharge (odds ratio, 0.6; 95 percent confidence interval, 0.4 to 1.0).

CONCLUSIONS

In patients who underwent total hip arthroplasty, a body-mass index of 25 or greater was associated with subsequent hospitalization for thromboembolism. Pneumatic compression in patients with a body-mass index of less than 25 and prophylaxis with warfarin after discharge were independently protective against thromboembolism.

Management and dosing of warfarin therapy

When initiating warfarin therapy, clinicians should avoid loading doses that can raise the International Normalized Ratio (INR) excessively; instead, warfarin should be initiated with a 5-mg dose (or 2 to 4 mg in the very elderly). With a 5-mg initial dose, the INR will not rise appreciably in the first 24 hours, except in rare patients who will ultimately require a very small daily dose (0.5 to 2.0 mg). Adjusting a steady-state warfarin dose depends on the measured INR values and clinical factors: the dose does not need to be adjusted for a single INR that is slightly out of range, and most changes should alter the total weekly dose by 5% to 20%. The INR should be monitored frequently (eg, 2 to 4 times per week) immediately after initiation of warfarin; subsequently, the interval between INR tests can be lengthened gradually (up to a maximum of 4 to 6 weeks) in patients with stable INR values. Patients who have an elevated INR will need more frequent testing and may also require vitamin K1. For example, a nonbleeding patient with an INR of 9 can be given low-dose vitamin K1 (eg, 2.5 mg phytonadione, by mouth). Patients who have an excessive INR with clinically important bleeding require clotting factors (eg, fresh-frozen plasma) as well as vitamin K1.

Temporary reversal of anticoagulation using oral vitamin K

Brief reversal of oral anticoagulant therapy is frequently necessary prior to minor surgery or invasive procedures. We sought to determine the effect of an oral dose of 2.0 mg of vitamin K(1) on the international normalized ratio (INR) among patients with a stable therapeutic INR who were maintained on their daily dose of warfarin. We prospectively studied a convenience cohort of patients attending an anticoagulation clinic who had either just completed treatment for venous thromboembolism or were receiving prophylaxis for atrial fibrillation, cardiomyopathy, or peripheral vascular disease. Each patient received an oral dose of 2.0 mg of aqueous vitamin K(1). Serial INR measurements were taken over 1 week. There was wide variation in the INR response between patients, from no change to complete reversal of anticoagulation. The effect also varied widely over time. There was a significant inverse correlation between the fall in logarithm of the INR and the daily warfarin dose required to achieve an INR value of 2.5 (r=-0.52, p=0.011). Use of a 2.0 mg oral dose of vitamin K(1) does not reliably reverse (correct) a therapeutic INR in patients maintained on their daily dose of warfarin.

Identification of the gene encoding sulfopyruvate decarboxylase, an enzyme involved in biosynthesis of coenzyme M

The products of two adjacent genes in the chromosome of Methanococcus jannaschii are similar to the amino and carboxyl halves of phosphonopyruvate decarboxylase, the enzyme that catalyzes the second step of fosfomycin biosynthesis in Streptomyces wedmorensis. These two M. jannaschii genes were recombinantly expressed in Escherichia coli, and their gene products were tested for the ability to catalyze the decarboxylation of a series of alpha-ketoacids. Both subunits are required to form an alpha(6)beta(6) dodecamer that specifically catalyzes the decarboxylation of sulfopyruvic acid to sulfoacetaldehyde. This transformation is the fourth step in the biosynthesis of coenzyme M, a crucial cofactor in methanogenesis and aliphatic alkene metabolism. The M. jannaschii sulfopyruvate decarboxylase was found to be inactivated by oxygen and reactivated by reduction with dithionite. The two subunits, designated ComD and ComE, comprise the first enzyme for the biosynthesis of coenzyme M to be described.

Identification of enzymes homologous to isocitrate dehydrogenase that are involved in coenzyme B and leucine biosynthesis in methanoarchaea

Two putative Methanococcus jannaschii isocitrate dehydrogenase genes, MJ1596 and MJ0720, were cloned and overexpressed in Escherichia coli, and their gene products were tested for the ability to catalyze the NAD- and NADP-dependent oxidative decarboxylation of DL-threo-3-isopropylmalic acid, threo-isocitrate, erythro-isocitrate, and homologs of threo-isocitrate. Neither enzyme was found to use any of the isomers of isocitrate as a substrate. The protein product of the MJ1596 gene, designated AksF, catalyzed the NAD-dependent decarboxylation of intermediates in the biosynthesis of 7-mercaptoheptanoic acid, a moiety of methanoarchaeal coenzyme B (7-mercaptoheptanylthreonine phosphate). These intermediates included (-)-threo-isohomocitrate [(-)-threo-1-hydroxy-1,2, 4-butanetricarboxylic acid], (-)-threo-iso(homo)(2)citrate [(-)-threo-1-hydroxy-1,2,5-pentanetricarboxylic acid], and (-)-threo-iso(homo)(3)citrate [(-)-threo-1-hydroxy-1,2, 6-hexanetricarboxylic acid]. The protein product of MJ0720 was found to be alpha-isopropylmalate dehydrogenase (LeuB) and was found to catalyze the NAD-dependent decarboxylation of one isomer of DL-threo-isopropylmalate to 2-ketoisocaproate; thus, it is involved in the biosynthesis of leucine. The AksF enzyme proved to be thermostable, losing only 10% of its enzymatic activity after heating at 100 degrees C for 10 min, whereas the LeuB enzyme lost 50% of its enzymatic activity after heating at 80 degrees C for 10 min.

A population-based study of the effectiveness of inferior vena cava filter use among patients with venous thromboembolism

BACKGROUND

There are few population-based data regarding the effectiveness of inferior vena cava filter use in the prevention of symptomatic pulmonary embolism.

OBJECTIVE

To determine the 1-year cumulative incidence of rehospitalization for venous thrombosis or pulmonary embolism among patients with thromboembolism treated with a vena cava filter compared with the incidence in a control population with thromboembolism.

PATIENTS AND METHODS

Population-based retrospective analysis of linked hospital discharge abstracts in California. From January 1, 1991, through December 30, 1995, 3632 patients were treated with a filter and 64,333 controls were admitted with a principal diagnosis of venous thromboembolism.

RESULTS

Filter-treated patients had significantly greater comorbidity, with a higher frequency of previous pulmonary embolism, recent major bleeding, malignant neoplasm, and stroke. Patients who initially manifested pulmonary embolism were significantly more likely to be rehospitalized for pulmonary embolism than patients with an initial diagnosis of venous thrombosis alone, among filter-treated patients (relative risk, 6.72; 95% confidence interval, 3.61-12.49) and controls (relative risk, 5.30; 95% confidence interval, 4.61-6.10). Risk-adjusted proportional hazards modeling showed no significant difference between filter-treated patients and controls in the relative hazard of rehospitalization for pulmonary embolism. However, filter placement was associated with a significantly higher relative hazard of rehospitalization for venous thrombosis among patients who initially manifested pulmonary embolism (relative hazard, 2.62; 95% confidence interval, 2.09-3.29), but not among those who presented with venous thrombosis (relative hazard, 1.14; 95% confidence interval, 0.92-1.43).

CONCLUSIONS

Insertion of a vena cava filter was not associated with a significant reduction in the 1-year incidence of rehospitalization for pulmonary embolism. Use of a filter was associated with a higher incidence of rehospitalization for venous thrombosis, but only among patients who initially manifested pulmonary embolism. A prospective clinical study is needed to determine the efficacy of filter use among patients with pulmonary embolism who do not meet strict guidelines for insertion of a vena cava filter.

Identification of an archaeal 2-hydroxy acid dehydrogenase catalyzing reactions involved in coenzyme biosynthesis in methanoarchaea

Two putative malate dehydrogenase genes, MJ1425 and MJ0490, from Methanococcus jannaschii and one from Methanothermus fervidus were cloned and overexpressed in Escherichia coli, and their gene products were tested for the ability to catalyze pyridine nucleotide-dependent oxidation and reduction reactions of the following alpha-hydroxy-alpha-keto acid pairs: (S)-sulfolactic acid and sulfopyruvic acid; (S)-alpha-hydroxyglutaric acid and alpha-ketoglutaric acid; (S)-lactic acid and pyruvic acid; and 1-hydroxy-1,3,4,6-hexanetetracarboxylic acid and 1-oxo-1,3,4, 6-hexanetetracarboxylic acid. Each of these reactions is involved in the formation of coenzyme M, methanopterin, coenzyme F(420), and methanofuran, respectively. Both the MJ1425-encoded enzyme and the MJ0490-encoded enzyme were found to function to different degrees as malate dehydrogenases, reducing oxalacetate to (S)-malate using either NADH or NADPH as a reductant. Both enzymes were found to use either NADH or NADPH to reduce sulfopyruvate to (S)-sulfolactate, but the V(max)/K(m) value for the reduction of sulfopyruvate by NADH using the MJ1425-encoded enzyme was 20 times greater than any other combination of enzymes and pyridine nucleotides. Both the M. fervidus and the MJ1425-encoded enzyme catalyzed the NAD(+)-dependent oxidation of (S)-sulfolactate to sulfopyruvate. The MJ1425-encoded enzyme also catalyzed the NADH-dependent reduction of alpha-ketoglutaric acid to (S)-hydroxyglutaric acid, a component of methanopterin. Neither of the enzymes reduced pyruvate to (S)-lactate, a component of coenzyme F(420). Only the MJ1425-encoded enzyme was found to reduce 1-oxo-1,3,4,6-hexanetetracarboxylic acid, and this reduction occurred only to a small extent and produced an isomer of 1-hydroxy-1,3,4,6-hexanetetracarboxylic acid that is not involved in the biosynthesis of methanofuran c. We conclude that the MJ1425-encoded enzyme is likely to be involved in the biosynthesis of both coenzyme M and methanopterin.

Optimization of inpatient warfarin therapy: impact of daily consultation by a pharmacist-managed anticoagulation service

OBJECTIVE

To determine the effect of daily consultation by a team of hospital pharmacists on the accuracy and rapidity of optimizing warfarin therapy.

DESIGN

Comparison of a historical control cohort with a prospective cohort matched for treatment indication.

SETTING

A 400-bed university teaching hospital.

PATIENTS

Sixty consecutive patients hospitalized in 1992 and starting warfarin for the first time, with anticoagulation therapy managed by physicians, were compared with 60 patients matched for warfarin indication hospitalized in 1995, but with anticoagulation therapy managed with pharmacy consultation.

RESULTS

Pharmacist management of initial warfarin therapy resulted in a significant reduction in the length of hospitalization compared with physician dosing, from 9.5 +/- 5.6 days to 6.8 +/- 4.4 days (p = 0.009). The number of patients and patient-days with international normalized ratio (INR) values >3.5 were reduced by pharmacist dosing from 37 patients and 142 days to 16 patients and 29 days, respectively (p < 0.001). Similarly, the number of patients and patient-days with INR >6.0 were reduced from 20 patients and 50 days to two patients and six days, respectively (p < 0.001). There were six documented bleeding complications in 1992 compared with one in 1995 (p = 0.11). The mean INR at discharge was significantly lower in the pharmacy surveillance group, 2.6 +/- 0.58, compared with the physician cohort, 3.3 +/- 2.1 (p = 0.07). Readmissions after discharge due to bleeding or recurrent thrombosis were reduced from five (at 1 mo) and 10 (at 3 mo) to two and five readmissions, respectively, by pharmacist intervention (p = 0.43). The number of patients with concurrently prescribed drugs known to significantly interact with warfarin was significantly lower (6 vs. 13; p = 0.02) in the pharmacy surveillance group.

CONCLUSIONS

Among patients starting warfarin for the first time, daily consultation by a pharmacist significantly decreased the length of hospital stay and the number of patients who received excessive anticoagulation therapy. These findings translate into improved quality of care and potentially significant cost savings.

A comparison of point-of-care instruments designed for monitoring oral anticoagulation with standard laboratory methods

Our study compared point-of-care (POC) device monitoring with traditional clinical laboratory methods device of patients on oral anticoagulant therapy. The POC devices used in the study were Coumatrak, CoaguChek, CoaguChek Plus, Thrombolytic Assessment System (TAS) PT-One, TAS PTNC, TAS PT, Hemachron Jr. Signature, ProTime Microcoagulation System, and Medtronics ACT II. The clinical laboratory method used thromboplastins with different ISI values: Innovin and Thromboplastin C Plus (TPC). All POC INRs showed strong correlation with both laboratory methods, with correlation coefficients of >0.900. All POC methods demonstrated a significant (p <0.05) difference in INR values, except the TAS PTNC and ACT II INRs (p: 0.12 and 0.71 respectively) when compared with Innovin INRs. All POC INRs were significantly different from TPC generated INRs (p <0.05). Comparisons of the POC INRs to the group mean of the POC methods, show higher correlation (R>0.93), but there were still significant (p<0.05) differences noted between the POC group INR mean and CoaguChek Plus, ACT II, TAS PT-One, TAS PTNC, and Hemachron Jr Signature INRs. These data indicate that POC INR biases exist between laboratory methods and POC devices. Until a suitable whole blood INR standardization method is available, we conclude that clinicians using point-of-care anticoagulation monitoring should be aware of differences between POC and parent laboratory values.

Coexistence of thin membrane and alport nephropathies in families with haematuria

The finding of familial haematuria without a history of deafness or renal impairment is often assumed to indicate a benign prognosis. However, we describe three families in whom Alport and thin basement membrane nephropathy were separately identified within the same pedigree. Our findings illustrate the importance of fully investigating families with haematuria, even if thin basement nephropathy has been diagnosed in one member.

Major bleeding after hospitalization for deep-venous thrombosis

PURPOSE

Most studies of oral anticoagulant-related bleeding have analyzed the incidence of adverse outcomes among patients with a variety of different conditions and without any comparison with a control group. We determined the incidence, time course, and risk factors associated with major bleeding after hospital discharge among patients with deep-vein thrombosis, and estimated the excess risk of bleeding associated with oral anticoagulant therapy.

METHODS

A total of 22,000 adults were hospitalized in California for 3 or more days with a diagnosis of deep-venous thrombosis between January 1, 1992, and September 30, 1994. We determined the risk factors associated with readmission for bleeding. We compared the incidence of readmission for bleeding with comparison cohorts of patients with pneumonia or cellulitis who were matched for age, gender, race, and length of hospital stay.

RESULTS

Of 21,250 patients with deep-venous thrombosis who were discharged without bleeding, 1.4% were readmitted for bleeding within 91 days; the rate was 2.7 times greater in the first 30 days than in the next 61 days. Risk factors for bleeding included hospitalization with gastrointestinal bleeding during the previous 18 months (relative hazard [RH] = 2.6, 95% confidence interval [CI]: 1.6 to 4.1), hospitalization with an alcohol-related diagnosis during the previous 18 months (RH = 2.6, 95% CI: 1.4 to 4.8), chronic renal disease (RH = 2.4, 95% CI: 1.4 to 4.2), female gender (RH = 1.7, 95% CI: 1.3 to 2.2), presence of a malignancy (RH = 1.6, 95% CI: 1.2 to 2.2), nonwhite race (RH = 1.6, 95% CI: 1.2 to 2.1), and age over 65 years (RH = 1.3, 95% CI: 1.0 to 1.7). Significantly more women (n = 40) had intracranial bleeding than men (n = 18, P = 0.02). In the comparison cohorts, the incidence of readmission for bleeding within 3 months of discharge was 0.7%, and the relative risk (RR) of readmission was greater in those with deep-venous thrombosis than in those with cellulitis (RR = 2.0, 95% CI: 1.6 to 2.5) or pneumonia (RR = 2.0, 95% CI: 1.7 to 2.5).

CONCLUSIONS

The incidence of rehospitalization for bleeding was greatest in the first 30 days after discharge, and was approximately twice that seen in patients hospitalized for cellulitis or pneumonia. Further studies are needed to determine why women and nonwhite patients are at increased risk for anticoagulant-related bleeding.

Identifying two ancient enzymes in Archaea using predicted secondary structure alignment

It is now possible to compare life forms at high levels of detail and completeness due to the increasing availability of whole genomes from all three domains. However, exploration of interesting hypotheses requires the ability to recognize a correspondence between proteins that may since have diverged beyond the threshold of detection by sequence-based methods. Since protein structure is far better conserved than protein sequence, structural information can enhance detection sensitivity, and this is the basis for the field of structural genomics. Demonstrating the effectiveness of this approach, we identify two important but previously elusive Archaeal enzymes: a homolog of dihydropteroate synthase and a thymidylate synthase. The former is especially noteworthy in that no Archaeal homolog of a bacterial folate biosynthetic enzyme has been found to date. Experimental confirmation of the deduced activity of both enzymes is described. Identification of two different proteins was attempted deliberately to help allay concern that predictive success is merely a lucky accident.

Oral anticoagulation in patients with atrial fibrillation: adherence with guidelines in an elderly cohort

PURPOSE

To determine adherence with practice guidelines in a population-based cohort of elderly persons aged 70 years or older with atrial fibrillation.

SUBJECTS AND METHODS

This was a cross-sectional analysis of a subgroup of participants in the Cardiovascular Health Study, a prospective observational study involving four communities in the United States. Subjects were participants with atrial fibrillation on electrocardiogram at one or more yearly examinations from 1993 to 1995. The outcome measure was self-reported use of warfarin in 1995.

RESULTS

In 1995, 172 (4.1%) participants had atrial fibrillation together with information regarding warfarin use and no preexisting indication for its use. Warfarin was used by 63 (37%) of these participants. Of the 109 participants not reporting warfarin use, 92 (84%) had at least one of the clinical risk factors (aside from age) associated with stroke in patients with atrial fibrillation. Among participants not taking warfarin, 47% were taking aspirin. Several characteristics were independently associated with warfarin use, including age [odds ratio (OR) = 0.6 per 5-year increment, 95% CI 0.5-0.9], a modified mini-mental examination score <85 points [OR = 0.3, 95% confidence interval (CI) 0.1-0.9], and among patients without prior stroke, female sex (OR = 0.5, 95% CI 0.2-1.0).

CONCLUSIONS

Despite widely publicized practice guidelines to treat patients who have atrial fibrillation with warfarin, most participants who had atrial fibrillation were at high risk for stroke but were not treated with warfarin. More studies are needed to determine why elderly patients with atrial fibrillation are not being treated with warfarin.

(R)-citramalate synthase in methanogenic archaea

The Methanococcus jannaschii gene MJ1392 was cloned, and its protein product was hyperexpressed in Escherichia coli. The resulting protein was purified and shown to catalyze the condensation of pyruvate and acetyl coenzyme A, with the formation of (R)-citramalate. Thus, this gene (cimA) encodes an (R)-citramalate synthase (CimA). This is the first identification of this enzyme, which is likely involved in the biosynthesis of isoleucine.

College of American Pathologists Conference XXXI on laboratory monitoring of anticoagulant therapy: laboratory monitoring of oral anticoagulant therapy

OBJECTIVE

To review the state of the art of laboratory monitoring of oral anticoagulant therapy, as reflected by the medical literature and the consensus opinion of recognized experts in the field, and to make recommendations for improvement in laboratory monitoring of oral anticoagulant therapy.

DATA SOURCES

Review of the medical literature, primarily from the last 10 years, and current laboratory practices by a panel of 8 international experts in the field of oral anticoagulant monitoring.

DATA EXTRACTION AND SYNTHESIS

After an initial assessment of the literature, key points were identified. Experts were assigned to do an in-depth review of the literature and current practices relevant to each of the key points and to prepare a summary of their findings and recommendations. A draft manuscript was prepared and circulated to every participant in the College of American Pathologists Conference XXXI on Laboratory Monitoring of Anticoagulant Therapy prior to the conference. Each of the key points and associated recommendations was then presented for discussion at the Conference. Recommendations were accepted if a consensus of the 26 experts attending the Conference was reached. The results of the discussion were used to revise the manuscript into its final form.

CONCLUSIONS

Consensus was reached on 12 recommendations concerning the laboratory monitoring of oral anticoagulant therapy. Detailed discussion of the rationale for each of these recommendations is found in the text of this article. Discussion of points on which consensus was not reached is also included in the text. It is hoped that widespread adoption of these recommendations will further improve the laboratory monitoring of oral anticoagulant therapy.

Mechanism for the enzymatic formation of 4-(beta-D-ribofuranosyl)aminobenzene 5'-phosphate during the biosynthesis of methanopterin

A central step in the biosynthesis of the modified folate methanopterin is the condensation of p-aminobenzoic acid (pAB) and 5-phospho-alpha-D-ribosyl-1-pyrophosphate (PRPP) which produce 4-(beta-D-ribofuranosyl)aminobenzene 5'-phosphate (beta-RFA-P) [White, R. H. (1996) Biochemistry 35, 3447-3456]. This reaction, catalyzed by the enzyme beta-RFA-P synthase, is unique among known phosphoribosyltransferases in that a decarboxylation of one of the substrates (pAB) occurs during the reaction and a C-riboside rather than an N-riboside is the product. In this work, the reaction catalyzed by the enzyme from Methanosarcina thermophila is shown to be analogous to other phosphoribosyltransferase reactions in that pyrophosphate is released as a product of the reaction, which is dependent upon magnesium ions. The molecular weight of the enzyme was estimated to be 65 000 using gel filtration chromatography, and the pH optimum was 4.8. Kinetic analysis indicated that the reaction involved a sequential pattern of substrate binding. Benzoic acid and several para-substituted benzoic acids inhibited beta-RFA-P synthase activity, while aniline, 4-aminobenzamide, and the methyl ester of pAB did not, indicating that an ionized carboxylic group plays a role in the binding of pAB. The observation that the enzyme was not inhibited by carbonyl reagents and that 4-hydroxybenzoic acid served as an alternate substrate, producing 4-(beta-D-ribofuranosyl)hydroxybenzene 5'-phosphate as the product, indicated that pyridoxal phosphate was not directly involved in the reaction mechanism. Incubation of the enzyme with PRPP and either pAB or 4-aminothiobenzoic acid in the presence of sodium cyanoborohydride led to the decreased production of beta-RFA-P and the accumulation of a reduced form of the proposed cyclohexadienimine reaction intermediates. These compounds were characterized by their acid-catalyzed decomposition which produces beta-D-ribofuranosylbenzene 5'-phosphate. On the basis of these results, a concerted mechanism is proposed for beta-RFA-P synthase in which an SN1-like reaction produces oxonium ion character at C-1 of PRPP which undergoes an ipso electrophilic aromatic substitution reaction at the carboxylic acid-bound carbon of pAB. Decarboxylation of the resulting cyclohexadienimine intermediate leads to the formation of beta-RFA-P.

Incidence and time course of thromboembolic outcomes following total hip or knee arthroplasty

BACKGROUND

Little is known about the incidence and time course of clinical thromboembolic events after total hip or knee arthroplasty, particularly after hospital discharge.

METHODS

We used a linked hospital discharge database provided by the State of California to identify cases diagnosed as having deep vein thrombosis or pulmonary embolism within 3 months of unilateral total hip or knee arthroplasty. Also, we surveyed orthopedic surgeons to estimate the frequency of postoperative thromboprophylaxis during July 1991 through June 1993. Medical charts were audited to determine the accuracy of the coded records.

RESULTS

Among 19,586 primary hip and 24,059 primary knee arthroplasties, the cumulative incidence of deep vein thrombosis or pulmonary embolism within 3 months of surgery was 556 (2.8%) after hip arthroplasty and 508 (2.1%) after knee arthroplasty. The diagnosis of thromboembolism was made after hospital discharge in 76% and 47% of the total hip and total knee arthroplasty cases, respectively (P<.001), with a median time of diagnosis of 17 days and 7 days after surgery, respectively (P<.001). Questionnaire results indicated that 95% of all cases received thromboprophylaxis and that the frequency, type, and duration of thromboprophylaxis was virtually identical after hip and knee arthroplasty.

CONCLUSIONS

There is a difference in the temporal patterns of clinically symptomatic thromboembolic complications after total hip and total knee arthroplasty, suggesting differences in pathogenesis or natural history. The findings suggest that to further reduce thromboembolic outcomes, earlier, more intense prophylaxis may be needed for total knee arthroplasty, and more prolonged prophylaxis may be required after total hip arthroplasty.

Alpha-keto acid chain elongation reactions involved in the biosynthesis of coenzyme B (7-mercaptoheptanoyl threonine phosphate) in methanogenic Archaea

The biochemistry of the 13 steps involved in the conversion of alpha-ketoglutarate and acetylCoA to alpha-ketosuberate, a precursor to the coenzymes coenzyme B (7-mercapto heptanoylthreonine phosphate) and biotin, has been established in Methanosarcina thermophila. These series of reactions begin with the condensation of alpha-ketoglutarate and acetylCoA to form trans-homoaconitate. The trans-homoaconitate is then hydrated and dehydrated to cis-homoaconitate with (S)-homocitrate serving as an intermediate. Rehydration of the cis-homoaconitate produces (-)-threo-isohomocitrate [(2R,3S)-1-hydroxy-1,2, 4-butanetricarboxylic acid], which undergoes a NADP+-dependent oxidative decarboxylation to produce alpha-ketoadipate. The resulting alpha-ketoadipate then undergoes two consecutive sets of alpha-ketoacid chain elongation reactions to produce alpha-ketosuberate. In each of these sets of reactions, it has been shown that the homologues of cis-homoaconitate, homocitrate, and (-)-threo-isohomocitrate serve as intermediates. The protein product of the Methanococcus jannaschii MJ0503 gene aksA (AksA) was found to catalyze the condensation of alpha-ketoglutarate and acetylCoA to form trans-homoaconitate. This gene product also catalyzed the condensation of alpha-ketoadipate or alpha-ketopimelate with acetylCoA to form, respectively, the (R)-homocitrate homologues of (R)-2-hydroxy-1,2,5-pentanetricarboxylic acid and (R)-2-hydroxy-1,2, 6-hexanetricarboxylic acid. The alpha-ketosuberate resulting from this series of reactions then undergoes a nonoxidative decarboxylation to form 7-oxoheptanoic acid, a precursor to coenzyme B, and an oxidative decarboxylation to form pimelate, the precursor to biotin. Of the 13 intermediates in this pathway, eight have not previously been reported as occurring in biological systems.

Renal biopsy diagnosis in children presenting with haematuria

We reviewed the clinical and renal biopsy findings in 322 children presenting during the years 1975-1996 with recurrent macro- or continuous microscopic haematuria persisting for > or =6 months, in whom non-glomerular causes were excluded. Family involvement was documented for first-degree relatives. All biopsies were examined by light microscopy, 317 by electron microscopy and 315 by immunofluorescence. Biopsies were classified as IgA nephropathy (78), Alport nephropathy (86), thin basement membrane nephropathy (TMN) (50), miscellaneous glomerulonephritis (32), hilar vasculopathy (28) and normal glomeruli (48). Although microscopic haematuria alone was more frequent in Alport nephropathy and TMN, the pattern of haematuria in individual patients did not predict histology. Of patients with familial haematuria, 79% of biopsies showed either Alport nephropathy or TMN. Hilar vasculopathy was observed both in isolation and in all abnormal histological categories.

Length of hospital stay for treatment of deep venous thrombosis and the incidence of recurrent thromboembolism

BACKGROUND

Current guidelines suggest that all patients with acute deep venous thrombosis should be treated with intravenous heparin for at least 5 days, overlapping with warfarin sodium for 4 to 5 days.

METHODS

Using linked state of California hospital discharge records from 1991 to 1994 we identified patients with acute deep venous thrombosis without pulmonary embolism, and determined the 6-month cumulative incidence of rehospitalization for recurrent thromboembolism. Coding was validated by reviewing the charts of 218 patients matched with the statewide data from 4 local hospitals.

RESULTS

A total of 36924 linked records met study criteria. In the validation group, objectively confirmed thrombosis that was treated with intravenous heparin followed by warfarin was noted in 20%, 65%, 94%, and 95% of the patients who were hospitalized for 2 or fewer days or 3, 4, or 5 or more days, respectively. Statewide, among patients hospitalized for 3, 4, 5, and 6 days, the 6-month cumulative incidence of hospitalization for recurrent thromboembolism was 5.4%, 5.1%, 5.4%, and 6.0%, respectively. Multivariate modeling of patients hospitalized for 3 to 10 days revealed that recurrent thromboembolism was associated with the length of hospitalization (odds ratio [OR], 1.06 each additional day; 95% confidence interval [CI], 1.04-1.08), presence of malignancy (OR, 1.58; 95% CI, 1.46-1.68), age (OR, 0.85 each 10 years; 95% CI, 0.84-0.86), dementia (OR, 0.38; 95% CI, 0.26-0.49), hospitalization for multiple injuries within 3 months (OR, 0.46; 95% CI, 0.32-0.60), and surgery within 3 months (OR, 0.84; 95% CI, 0.78-0.90).

CONCLUSIONS

We found no evidence that a stay of 4 days for treatment of deep venous thrombosis was associated with a higher rate of recurrent thromboembolism compared with hospitalization for 5 or more days. Although the evidence was not as strong, the incidence of recurrent thromboembolism after a stay of 3 days appeared comparable with that after a stay of 5 days. These findings suggest that fewer than 5 days of intravenous heparin overlapping with warfarin may provide effective initial treatment for deep venous thrombosis among patients deemed ready for hospital discharge.

Incidence of idiopathic deep venous thrombosis and secondary thromboembolism among ethnic groups in California

BACKGROUND

Few studies have compared the incidence of deep venous thrombosis among ethnic groups.

OBJECTIVE

To determine the incidence of deep venous thrombosis among ethnic groups.

DESIGN

Analysis of the linked California Patient Discharge Data Set from 1991 to 1994.

SETTING

California.

PATIENTS

17991 patients with idiopathic deep venous thrombosis (thrombosis without cancer or hospitalization within preceding 6 months) and 5573 patients with secondary thromboembolism (thromboembolism occurring within 3 months of seven different events).

MEASUREMENTS

Ethnicity was determined by using race as documented in the data set. For idiopathic deep venous thrombosis, standardized age- and sex-adjusted incidences were calculated. For secondary thromboembolism, proportional hazards modeling was done.

RESULTS

The annual incidence of idiopathic deep venous thrombosis per 1000000 persons older than 18 years of age was 230 for white persons, 293 for African Americans (rate ratio, 1.27 [95% CI, 1.07 to 1.51]), 139 for Hispanic persons (rate ratio, 0.60 [CI, 0.54 to 0.67]), and 60 for Asians and Pacific Islanders (rate ratio, 0.26 [CI, 0.22 to 0.30]). Compared with white persons, Asians and Pacific Islanders who developed secondary thromboembolism had a significantly lower relative risk (range, 0.22 to 0.61) for all seven conditions analyzed.

CONCLUSIONS

Compared with white persons, Asians and Pacific Islanders have a very low incidence of idiopathic deep venous thrombosis and a very low relative risk for secondary venous thromboembolism.

Methanopterin biosynthesis: methylation of the biosynthetic intermediates

The basic scheme for the biosynthesis of methanopterin (MPT) in Methanobacterium thermoautotrophicum strain DeltaH, and M. thermoautotrophicum strain Marburg, has been shown to be the same as that recently determined for Methanosarcina thermophila strain TM-1. This scheme has, as one of its unique steps, the condensation of 4-aminobenzoic acid with 5-phospho-alpha-d-ribosyl diphosphate (PRPP) to form 4-(beta-d-ribofuranosyl)aminobenzene 5'-phosphate (beta-RFA-P). Labeling experiments with each of these organisms have established that the sites in the overall sequence of reactions from beta-RFA-P to MPT, where the S-adenosylmethionine-dependent C-9 and C-7 methylations of the pterin-containing intermediates occur, are organism related. In this work, cell extracts of M. thermoautotrophicum strain DeltaH, and M. thermoautotrophicum strain Marburg were found to contain significant amounts of methanopterin lacking the phosphate and 2-hydroxyglutaric acid groups.

Purification and properties of serine hydroxymethyltransferase from Sulfolobus solfataricus

Serine hydroxymethyltransferase (SHMT) catalyzes the reversible cleavage of serine to glycine with the transfer of the one-carbon group to tetrahydrofolate to form 5,10-methylenetetrahydrofolate. No SHMT has been purified from a nonmethanogenic Archaea strain, in part because this group of organisms uses modified folates as the one-carbon acceptor. These modified folates are not readily available for use in assays for SHMT activity. This report describes the purification and characterization of SHMT from the thermophilic organism Sulfolobus solfataricus. The exchange of the alpha-proton of glycine with solvent protons in the absence of the modified folate was used as the activity assay. The purified protein catalyzes the synthesis of serine from glycine and a synthetic derivative of a fragment of the natural modified folate found in S. solfataricus. Replacement of the modified folate with tetrahydrofolate did not support serine synthesis. In addition, this SHMT also catalyzed the cleavage of both allo-threonine and beta-phenylserine in the absence of the modified folate. The cleavage of these two amino acids in the absence of tetrahydrofolate is a property of other characterized SHMTs. The enzyme contains covalently bound pyridoxal phosphate. Sequences of three peptides showed significant similarity with those of peptides of SHMTs from two methanogens.

Effect of weight, sex, age, clinical diagnosis, and thromboplastin reagent on steady-state intravenous heparin requirements

BACKGROUND

There is a significant direct relationship between steady-state intravenous heparin dose requirements and total body weight. Less is known about whether sex, age, clinical diagnosis, and the thromboplastin used to measure the activated partial thromboplastin time (aPTT) affect heparin dose requirements.

METHODS

Four cohorts of patients treated with intravenous heparin were gathered from 3 hospitals: 2 cohorts with deep vein thrombosis (DVT) and 2 cohorts with coronary artery disease (CAD). For each clinical diagnosis, half the patients were monitored using one aPTT reagent and the remainder were monitored using a second reagent. Heparin doses and aPTT measurements were recorded, and the dose necessary to achieve an aPTT ratio of 2.0 was calculated using a computer software program.

RESULTS

We analyzed the records of 340 patients: 165 with DVT and 175 with CAD. Using analysis of variance, there was a significant difference in the steady-state heparin requirements among patients with DVT compared with patients with CAD (P < .001). For each clinical diagnosis, the use of a different thromboplastin reagent did not affect heparin dose requirements (P > .42). Linear regression modeling disclosed that the steady-state heparin dose for patients with DVT was a function of weight plus an effect modifier involving weight and age, whereas for patients with CAD there was only a weak relationship with weight.

CONCLUSIONS

Steady-state heparin dose requirements were significantly different in patients with DVT compared with patients with CAD, suggesting that different dosing nomograms are needed for each condition. For patients with DVT, the accuracy of the initial heparin dose estimate may be improved by considering the patient's age and weight.

Biosynthesis of the peptide bond in the coenzyme N-(7-mercaptoheptanoyl)-L-threonine phosphate

The biochemical mechanism for the formation of the amide bond in N-(7-mercaptoheptanoyl)-L-threonine phosphate (HS-HTP) has been studied by measuring the incorporation of L-[3-(3)H]threonine into N-(7-mercaptoheptanoyl)-L-threonine (HS-HT) by cell extracts (CE) of Methanosarcina thermophila incubated with different precursors. Synthesis of HS-HT was observed from L-[3-(3)H]threonine and 7-mercaptoheptanoic acid (HS-H) when the incubations were conducted with either crude CE or Sephadex column-purified CE. In the presence of CE, the synthesis of HS-HT was found to be inhibited 66% by preincubation of the extract with ATPase, indicating that ATP was involved in the biosynthesis. In spite of this indication of ATP involvement in the coupling reaction, incubation of the crude CE with L-[3-(3)H]threonine, HS-H, and ATP was found to inhibit the formation of HS-HT. In contrast, the synthesis of HS-HT in the presence of Sephadex column-purified CE was found to be stimulated by the addition of ATP. Incubation of the crude CE with the CoA thioester of 7-mercaptoheptanoic acid (HS-HCoA) or the mixed disulfide formed between coenzyme M and 7-mercaptoheptanoic acid did not stimulate the biosynthesis. The biosynthesis of HS-HT was found to be strongly inhibited by an ethanol extract of the crude CE. This inhibition was found to be attributed to the HS-HTP present in the extract. Stimulation of HS-HT biosynthesis 300-fold was observed when the Sephadex column-purified CE was incubated with L-[3-(3)H]threonine and 7-mercaptoheptanoyl phosphate (HS-H-P). Data indicate that HS-HT is produced by the phosphorylation of HS-H to HS-H-P with ATP, which then reacts with L-threonine to produce HS-HT.

Purification of the Azotobacter vinelandii nifV-encoded homocitrate synthase

The nifV gene product (NifV) from Azotobacter vinelandii was recombinantly expressed at high levels in Escherichia coli and purified. NifV is a homodimer that catalyzes the condensation of acetyl coenzyme A (acetyl-CoA) and alpha-ketoglutarate. Although alpha-ketoglutarate supports the highest level of activity, NifV will also catalyze the condensation of acetyl-CoA and certain other keto acids. E. coli cells in which a high level of nifV expression is induced excrete homocitrate into the growth medium.

Three opsin-encoding cDNAS from the compound eye of Manduca sexta

Three distinct opsin-encoding cDNAs, designated MANOP1, MANOP2 and MANOP3, were isolated from the retina of the sphingid moth Manduca sexta. MANOP1 codes for a protein with 377 amino acid residues. It is similar in sequence to members of a phylogenetic group of long-wavelength-sensitive arthropod photopigments, most closely resembling the opsins of ants, a praying mantis, a locust and the honeybee. MANOP2 and MANOP3 opsins have 377 and 384 residues respectively. They belong to a related group of insect visual pigments that include the ultraviolet-sensitive rhodopsins of flies as well as other insect rhodopsins that are also thought to absorb at short wavelengths. The retina of Manduca sexta contains three rhodopsins, P520, P450 and P357, with absorbance peaks, respectively, at green, blue and ultraviolet wavelengths. There is evidence that MANOP1 encodes the opsin of P520. We suggest that MANOP2 encodes P357 and that MANOP3, representing a class of blue-sensitive insect photopigments, encodes P450.

D-erythro-neopterin biosynthesis in the methanogenic archaea Methanococcus thermophila and Methanobacterium thermoautotrophicum deltaH

The steps in the biosynthetic transformation of GTP to 7,8-dihydro-D-erythro-neopterin (H2neopterin), the precursor to the modified folates found in the methanogenic archaea, has been elucidated for the first time in two members of the domain Archaea. In Methanococcus thermophila and Methanobacterium thermoautotrophicum deltaH, it has been demonstrated that H2neopterin 2':3'-cyclic phosphate is an intermediate in this conversion. In addition, the formation of the pterin ring of the H2neopterin 2':3'-cyclic phosphate is catalyzed not by a single enzyme, as is known to occur with GTP cyclohydrolase I in the Eucarya and Bacteria, but rather by two or more enzymes. A 2,4,5-triamino-4(3H)-pyrimidinone-containing molecule, most likely 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5'-triphosphate, has been identified as an intermediate in the formation of the H2neopterin 2':3'-cyclic phosphate. Synthetic H2neopterin 2':3'-cyclic phosphate was found to be readily hydrolyzed by cell extracts of M. thermophila via the H2neopterin 3'-phosphate to H2neopterin, a known precursor to the pterin portion of methanopterin.

Regional specialization in the eye of the sphingid moth Manduca sexta: blue sensitivity of the ventral retina

The compound eye of the tobacco hornworm moth Manduca sexta contains green-, blue-, and ultraviolet-sensitive photoreceptors. Electroretinogram spectral-sensitivity measurements were recorded from different regions of the retina in order to broadly map the distribution of the three receptor types. The relative contribution of the three receptors to spectral-sensitivity curves was estimated by fitting theoretical curves based on the absorption spectra of the three rhodopsins. This analysis indicated that the dorsal retina is green and ultraviolet dichromatic, with green-sensitive cells greatly predominating. The ventral retina is trichromatic with a substantial population of blue- and ultraviolet-sensitive receptors. We previously showed that flower visitation for nectar feeding is mediated mainly by blue-sensitive cells. Their localization in the ventral retina seems an appropriate adaptation of the receptor mosaic, since the moths hover above flowers as they feed.

Purine biosynthesis in the domain Archaea without folates or modified folates

The established pathway for the last two steps in purine biosynthesis, the conversion of 5-aminoimidazole-4-carboxamide ribonucleotide (ZMP) to IMP, is known to utilize 10-formyl-tetrahydrofolate as the required C1 donor cofactor. The biosynthetic conversion of ZMP to IMP in three members of the domain Archaea, Methanobacterium thermoautotrophicum deltaH, M. thermoautotrophicum Marburg, and Sulfolobus solfataricus, however, has been demonstrated to occur with only formate and ATP serving as cofactors. Thus, in these archaea, which use methanopterin (MPT) or another modified folate in place of folate as the C1 carrier coenzyme, neither folate nor a modified folate serves as a cofactor for this biosynthetic transformation. It is concluded that archaea, which function with modified folates such as MPT, are able to carry out purine biosynthesis without the involvement of folates or modified folates.

Occurrence and biosynthesis of 5-aminoimidazole-4-carboxamide ribonucleotide and N-(beta-D-ribofuranosyl)formamide 5'-phosphate in Methanobacterium thermoautotrophicum delta(H)

5-Aminoimidazole-4-carboxamide ribonucleotide (ZMP) and N-(beta-D-ribofuranosyl)formamide 5'-phosphate (FAR-P) have been identified as products of the metabolism of ATP and 5-phospho-alpha-D-ribosyl diphosphate by Methanobacterium thermoautotrophicum delta(H), a member of the domain Archaea. Evidence indicates that the first three steps in the pathway to the formation of these compounds are the same as the first three steps of histidine biosynthesis and lead to the generation of pro-phosphoribosyl formimino-5-aminoimidazole-4-carboxamide ribonucleotide (5'-proFAR). The 5'-proFAR then undergoes hydrolysis to ZMP and FAR-P. The reaction was detected by an unexpected high concentration of ZMP in cell extracts of M. thermoautotrophicum delta(H).

Sex differences in sensory and motor branches of the pudendal nerve of the rat

The morphology of the pudendal nerve was quantified in adult male and female rats. The sensory branch of the pudendal nerve was about three times as large in cross section in males as in females, and the motor branch was about five times as large. Electron microscopy was used to determine the ultrastructural bases of these gross size differences. Differences that were found included greater packing density of both myelinated and unmyelinated axons in females, larger myelinated and unmyelinated axons in males, larger myelin sheaths of sensory axons in males, more numerous myelinated axons in both branches of males, and more numerous unmyelinated axons in the sensory branch of males. There was also some indication that myelinated sensory axons were more likely to branch in the dorsal clitoral nerve of females than in the homologous nerve of males. Morphological differences in the structure of pudendal axons, their associated Schwann cells, and the extracellular matrix as well as differences in sensory and motor axonal number all have potential implications for the sexual differentiation of the central nervous system and behavior.

Day care renal biopsy

Over the 6 years 1989-1994, 384 percutaneous renal biopsies were performed, 329 on native and 55 on transplanted kidneys. Biopsy was undertaken on a day care basis in 304 instances (79.2%). Failure to obtain 5 or more glomeruli was experienced in 23 (6.0%) of the 304 day care biopsies. There were no significant differences in technical failure rates between day care patients and inpatients, local analgesia and general anaesthetic, or native and transplanted kidneys, but a higher rate was observed in biopsies performed unaided by trainees than by experienced operators (P = 0.002). Six patients were detained overnight for minor complications and a seventh for unrelated reasons. Two patients discharged on the day of biopsy despite gross haematuria were readmitted 8-10 days later with secondary haemorrhage. The complication rate of 2.6% compares favourably with published data. Few paediatric renal units currently perform day care renal biopsy, and we recommend its wider acceptance.

Dawn, diacylglycerol, calcium, and protein kinase C--the retinal wrecking crew. A signal transduction cascade for rhabdom shedding in the Limulus eye

Vertebrate and invertebrate photoreceptors shed their photosensitive membrane on a daily basis. Although we have detailed knowledge of the morphology of the disc shedding and renewal process in vertebrate photoreceptors, and of the turnover of rhabdom in invertebrate photoreceptors, we know relatively little about the molecular mechanisms whereby these processes are triggered by light and/or by circadian efferent input to the retina. We have used the horseshoe crab, Limulus polyphemus, as a model system to unravel the molecular means by which the trigger light is communicated to the intracellular machinery responsible for the daily breakdown of the photosensitive membrane. Phorbol esters, potent and specific activators of protein kinase C (PKC), induce a robust burst of rhabdom shedding when injected subretinally into the compound lateral eye of Limulus. This occurs in the absence of the light trigger normally required to initiate shedding in the lateral eye at dawn, suggesting that PKC may play a role in the light triggering of rhabdom shedding. Diacylglycerol (DAG) analogs were also found to elicit rhabdom shedding in the lateral eye without a light trigger, but at uncharacteristically high concentrations. However, injecting inositol trisphosphate (InsP3) and DAG analog simultaneously results in a tenfold decrease in the concentration of DAG analog required to initiate a shedding event. Immunohistochemical screening for PKC in the lateral eye shows that two isozymes (PKC beta II and PKC zeta) are co-localized to the retinular cell rhabdom. Taken together, these data suggest that light triggers rhabdom shedding at dawn via a classical Ca(2+)-sensitive PKC, similar to PKC beta II, which is activated synergistically by the light-evoked production of DAG and InsP3.