Diagnostic models predicting paediatric viral acute respiratory infections: a systematic review

OBJECTIVES

To systematically review and evaluate diagnostic models used to predict viral acute respiratory infections (ARIs) in children.

DESIGN

Systematic review.

DATA SOURCES

PubMed and Embase were searched from 1 January 1975 to 3 February 2022.

ELIGIBILITY CRITERIA

We included diagnostic models predicting viral ARIs in children (<18 years) who sought medical attention from a healthcare setting and were written in English. Prediction model studies specific to SARS-CoV-2, COVID-19 or multisystem inflammatory syndrome in children were excluded.

DATA EXTRACTION AND SYNTHESIS

Study screening, data extraction and quality assessment were performed by two independent reviewers. Study characteristics, including population, methods and results, were extracted and evaluated for bias and applicability using the Checklist for Critical Appraisal and Data Extraction for Systematic Reviews of Prediction Modelling Studies and PROBAST (Prediction model Risk Of Bias Assessment Tool).

RESULTS

Of 7049 unique studies screened, 196 underwent full text review and 18 were included. The most common outcome was viral-specific influenza (n=7; 58%). Internal validation was performed in 8 studies (44%), 10 studies (56%) reported discrimination measures, 4 studies (22%) reported calibration measures and none performed external validation. According to PROBAST, a high risk of bias was identified in the analytic aspects in all studies. However, the existing studies had minimal bias concerns related to the study populations, inclusion and modelling of predictors, and outcome ascertainment.

CONCLUSIONS

Diagnostic prediction can aid clinicians in aetiological diagnoses of viral ARIs. External validation should be performed on rigorously internally validated models with populations intended for model application.

PROSPERO REGISTRATION NUMBER

CRD42022308917.

Weight loss in achalasia is determined by its phenotype

Patients with achalasia present with dysphagia, regurgitation, and varying degrees of weight loss. However, despite it being a disorder of the lower esophageal sphincter with functional obstruction in all patients, it is unclear why certain patients lose significantly more weight compared to others. The aims of this study are to assess demographic, clinical, and manometric characteristics of a large cohort of patients with achalasia to determine potential correlates of weight loss in this population. Patients with diagnosis of achalasia referred to our center between 2009 and 2016 were evaluated. Demographic and physiologic tests between those with and without weight loss were compared. The cohort of patients with initial self-reported weight loss were studied to determine change in weight after intervention (pneumatic dilation or myotomy). The Kruskal-Wallis test was used for comparison of continuous variables between groups and Pearson's χ2 test was used for comparison of categorical variables between groups. 138 patients with achalasia were evaluated. 35 patients were excluded due to lack of manometric data and 3 from lack of documented weight resulting in the study population of 100 patients with achalasia [51% male, median age: 56 years]. Weight loss was reported in 51/100 (51%) patients. BMI was lower in patients who reported weight loss (25 vs. 31, P < 0.001) with a median weight loss of 28 lbs (14-40 lbs). There were no significant differences in age at diagnosis, gender, or symptom presentation (dysphagia, regurgitation, or chest pain) between the groups. However, more patients with type II achalasia (63%) reported weight loss as compared to other sub-types (P = 0.013). 73% of type III achalasia denied having weight loss. Patients who denied weight loss had symptoms for longer duration (24 vs. 12 months, P < 0.001) and had lower mean residual LES pressure (20 vs. 30 mmHg, P = 0.006). Postintervention 42% of patients reported no weight regain despite appropriate therapy for achalasia with median follow-up of 22 months (range: 6-90 months). Type II achalasia patients are most likely and type III achalasia are least likely to have weight loss compared to type I achalasia. Given that no other demographic/physiologic parameters predicted weight loss, the role of underlying inflammatory cascade in achalasia phenotypes deserves special attention.

Symptom association probability does not reliably distinguish functional heartburn from reflux hypersensitivity

BACKGROUND

Symptom association probability (SAP) is thought to distinguish reflux hypersensitivity from functional disorders. A diagnosis of hypersensitive oesophagus (SAP-positive) indicates that gastro-oesophageal reflux disease (GERD) is the cause of continued symptoms.

AIM

To conduct an analysis of pH and symptom criteria that lead to a diagnosis of SAP-positivity METHODS: We calculated SAP for 205 patients with GERD symptoms refractory to proton pump inhibitor (PPI) therapy who underwent endoscopy with wireless pH monitoring from 2007 to 2014. Patients were divided into three groups: pH-negative with no oesophagitis (n = 45), pH-positive with no oesophagitis (n = 130), and patients with oesophagitis (n = 30). We constructed a 2 × 2 table of symptom and reflux event association and quantified the number of 2-minute intervals for each of the 2 × 2 variables that distinguished SAP-positive from SAP-negative. In a separate cohort of 58 patients who had undergone anti-reflux surgery, we evaluated the effects of pre-surgery SAP.

RESULTS

The difference in symptom association parameters that led to a diagnosis of an SAP-positive was small (2.98% in oesophagitis-positive; 1.56% in oesophagitis-negative/pH-positive; 0.48% in oesophagitis-negative/pH-negative). In the pH-negative/oesophagitis-negative group, a difference of 0.48% led to a diagnosis of hypersensitivity. There was significant variability in SAP values between day 1 and day 2 of pH testing in all groups, with the greatest in the oesophagitis-positive group, despite objective evidence for reflux (27% in oesophagitis-positive, 19% pH-positive/oesophagitis-negative, and 7% in pH-negative/oesophagitis-negative). Pre-surgery SAP was not associated with response to anti-reflux surgery.

CONCLUSION

In PPI-refractory GERD, SAP cannot accurately distinguish reflux hypersensitivity from functional oesophageal symptoms.

Randomized controlled trial comparing esophageal dilation to no dilation among adults with esophageal eosinophilia and dysphagia

The role of esophageal dilation in patients with esophageal eosinophilia with dysphagia remains unknown. The practice of dilation is currently based on center preferences and expert opinion. The aim of this study is to determine if, and to what extent, dysphagia improves in response to initial esophageal dilation followed by standard medical therapies. We conducted a randomized, blinded, controlled trial evaluating adult patients with dysphagia and newly diagnosed esophageal eosinophilia from 2008 to 2013. Patients were randomized to dilation or no dilation at time of endoscopy and blinded to dilation status. Endoscopic features were graded as major and minor. Subsequent to randomization and endoscopy, all patients received fluticasone and dexlansoprazole for 2 months. The primary study outcome was reduction in overall dysphagia score, assessed at 30 and 60 days post-intervention. Patients with severe strictures (less than 7-mm esophageal diameter) were excluded from the study. Thirty-one patients were randomized and completed the protocol: 17 randomized to dilation and 14 to no dilation. Both groups were similar with regard to gender, age, eosinophil density, endoscopic score, and baseline dysphagia score. The population exhibited moderate to severe dysphagia and moderate esophageal stricturing at baseline. Overall, there was a significant (P < 0.001) but similar reduction in mean dysphagia score at 30 and 60 days post-randomization compared with baseline in both groups. No significant difference in dysphagia scores between treatment groups after 30 (P = 0.93) or 60 (P = 0.21) days post-intervention was observed. Esophageal dilation did not result in additional improvement in dysphagia score compared with treatment with proton pump inhibitor and fluticasone alone. In patients with symptomatic esophageal eosinophilia without severe stricture, dilation does not appear to be a necessary initial treatment strategy.

Increasing F2-isoprostanes in the first month after birth predicts poor respiratory and neurodevelopmental outcomes in very preterm infants

OBJECTIVE

This study examined the association between increased early oxidative stress, measured by F2-isoprostanes (IsoPs), and respiratory morbidity at term equivalent age and neurological impairment at 12 months of corrected age (CA).

STUDY DESIGN

Plasma samples were collected from 136 premature infants on days 14 and 28 after birth. All participants were infants born at ⩽28 weeks of gestational age enrolled into the Prematurity and Respiratory Outcomes Program (PROP) study. Respiratory morbidity was determined at 40 weeks of postmenstrual age (PMA) by the Respiratory Severity Index (RSI), a composite measure of oxygen and pressure support. Neurodevelopmental assessment was performed using the Developmental Assessment of Young Children (DAYC) at 12 months of CA. Multivariable logistic regression models estimated associations between IsoP change, RSI and DAYC scores. Mediation analysis was performed to determine the relationship between IsoPs and later outcomes.

RESULTS

Developmental data were available for 121 patients (90% of enrolled) at 12 months. For each 50-unit increase in IsoPs, regression modeling predicted decreases in cognitive, communication and motor scores of -1.9, -1.2 and -2.4 points, respectively (P<0.001). IsoP increase was also associated with increased RSI at 40 weeks of PMA (odds ratio=1.23; P=0.01). RSI mediated 25% of the IsoP effect on DAYC motor scores (P=0.02) and had no significant impact on cognitive or communication scores.

CONCLUSIONS

In the first month after birth, increases in plasma IsoPs identify preterm infants at risk for respiratory morbidity at term equivalent age and worse developmental outcomes at 12 months of CA. Poor neurodevelopment is largely independent of respiratory morbidity.

Neuroimaging identifies increased manganese deposition in infants receiving parenteral nutrition

BACKGROUND

Manganese, an essential metal for normal growth and development, is neurotoxic on excessive exposure. Standard trace element-supplemented neonatal parenteral nutrition (PN) has a high manganese content and bypasses normal gastrointestinal absorptive control mechanisms, which places infants at risk of manganese neurotoxicity. Magnetic resonance (MR) relaxometry demonstrating short T1 relaxation time (T1R) in the basal ganglia reflects excessive brain manganese accumulation.

OBJECTIVE

This study tested the hypothesis that infants with greater parenteral manganese exposure have higher brain manganese accumulation, as measured by MR imaging, than do infants with lower parenteral manganese exposure.

DESIGN

Infants exposed to parenteral manganese were enrolled in a prospective cohort study. Infants classified as having high manganese exposure received >75% of their nutrition in the preceding 4 wk as PN. All others were classified as having low exposure. Daily parenteral and enteral manganese intakes were calculated. Whole-blood manganese was measured by high-resolution inductively coupled plasma mass spectrometry. Brain MR relaxometry was interpreted by a masked reviewer. Linear regression models, adjusted for gestational age (GA) at birth, estimated the association of relaxometry indexes with total and parenteral manganese exposures.

RESULTS

Seventy-three infants were enrolled. High-quality MR images were available for 58 infants, 39 with high and 19 with low manganese exposure. Four infants with a high exposure had blood manganese concentrations >30 μg/L. After controlling for GA, higher parenteral and total manganese intakes were associated with a lower T1R (P = 0.01) in the globus pallidus and putamen but were not associated with whole-blood manganese (range: 3.6-56.6 μg/L). Elevated conjugated bilirubin magnified the association between parenteral manganese and decreasing T1R.

CONCLUSION

A short T1R for GA identifies infants at risk of increased brain manganese deposition associated with PN solutions commonly used to nourish critically ill infants. These trials were registered at clinicaltrials.gov as NCT00392977 and NCT00392730.

Volume guarantee pressure support ventilation in extremely preterm infants and neurodevelopmental outcome at 18 months

OBJECTIVE

Compared with pressure-controlled ventilation (PCV), volume-targeted ventilation is associated with decreased neonatal complications, including the combined outcome of death or bronchopulmonary dysplasia. However, little is known about its effect on neurodevelopmental outcome. We evaluated the hypothesis that as compared with PCV, volume-targeted ventilation reduces the risk of the combined outcome of neurodevelopmental impairment or death in very low birth weight infants.

STUDY DESIGN

We studied a cohort of extremely preterm infants managed with either volume guarantee pressure support ventilation (VGPSV; n=135) or PCV (n=135). Infants were evaluated at 18 months adjusted age with a standardized neurological examination and the Bayley Scales of Infant and Toddler Development-third edition. Logistic regression models were used to evaluate the association of ventilation mode and neurodevelopmental outcome.

RESULT

Rates of pulmonary interstitial emphysema (odds ratio 0.6; 95% confidence limits: 0.4, 0.8), hypotension (odds ratio: 0.7; 95% confidence limits: 0.5, 0.9) and mortality (odds ratio 0.45; 95% confidence limits: 0.22, 0.9) were lower among infants treated with VGPSV. The infants in the VGPSV group had a significantly shorter duration on mechanical ventilation compared with infants in the PCV group (log-rank test P<0.01). Seventy percent (155/221) of survivors were evaluated at 18 months adjusted age. A trend towards benefit for the combined outcome of death or neurodevelopmental impairment was seen in the VGPSV group but did not reach statistical significance (odds ratio: 0.59; 95% confidence limits: 0.32, 1.08).

CONCLUSION

VGPSV was associated with a decreased risk of short-term complications but not long-term developmental impairment in this modest-sized cohort.

Adverse neurodevelopmental outcomes after exposure to phenobarbital and levetiracetam for the treatment of neonatal seizures

OBJECTIVE

Compare neurodevelopment after levetiracetam (LEV) and phenobarbital (PB) for neonatal seizures.

STUDY DESIGN

Retrospective study of infants who received antiepileptic drugs (AEDs) for neonatal seizures. Effect of cumulative exposure to LEV and PB on outcomes of death, cerebral palsy (CP) and Bayley Scales of Infant Development (BSID) scores were evaluated at 24 months corrected age. Analyses were adjusted for number of electrographic seizures and gestational age.

RESULT

In 280 infants with comparable seizure etiology and cranial imaging results, increased exposure to PB was associated with worse BSID cognitive and motor scores (8.1- and 9-point decrease per 100 mg kg(-1); P=0.01). The effect was less with LEV (2.2- and 2.6-point decrease per 300 mg kg(-1) LEV (P=0.01)). CP probability increased by 2.3-fold per 100 mg kg(-1) PB and was not associated with increasing LEV.

CONCLUSION

Increased exposure to PB is associated with worse neurodevelopmental outcomes than LEV. Prospective studies of outcomes of neonatal exposure to AEDs are essential.

An oropharyngeal pH monitoring device to evaluate patients with chronic laryngitis

BACKGROUND

Diagnostics for gastro-esophageal reflux disease (GERD) are suboptimal because of limited sensitivity. We performed in vitro and in vivo studies to systematically assess the performance characteristics of an oropharyngeal pH probe.

METHODS

In vitro studies compared the oropharyngeal probe with a standard pH catheter in liquid and aerosolized solutions, pH 1-7. The accuracy of measurements, deviation from target pH, and time to equilibrium pH were determined. Simultaneous distal esophageal pH measurements were obtained in 11 patients with GERD. Oropharyngeal and distal esophageal reflux parameters were measured for controls (n = 20), patients with GERD (n = 17), and patients with chronic laryngitis (n = 10).

KEY RESULTS

In the liquid phase, at pH 4-5, the oropharyngeal probe had less deviation from the target value than the standard catheter; deviation in the vapor phase was similar (0.4 pH units). Median (interquartile) time to reach equilibrium pH was significantly (P < 0.001) faster with the oropharyngeal than the standard probe. In comparing simultaneous distal esophageal pH characteristics, 96% of recordings with the new and standard probes were in agreement to within ± 1.0 pH unit; 71% of recordings were in agreement within ± 0.5 pH units. Patients with chronic laryngitis had significantly higher levels of oropharyngeal acid exposure at pH <4, <5, and <6, in the upright position than patients with GERD or controls (P < .001).

CONCLUSIONS & INFERENCES

Oropharyngeal pH monitoring appears to be more sensitive than traditional pH monitoring in evaluation of patients with extraesophageal reflux. It is a promising tool in evaluation of this difficult group of patients.

Necrotizing enterocolitis in infants with periventricular hemorrhagic infarction: associations and outcomes

BACKGROUND

Necrotizing enterocolitis (NEC) and periventricular hemorrhagic infarction (PVHI) are complications of prematurity associated with poor neurodevelopmental outcomes.

OBJECTIVES

We characterized temporal and causal associations between NEC and type of PVHI as well as associations with outcomes.

METHODS

This was a multicenter retrospective study of infants with birth weight <1,500 g and diagnosis of PVHI by a pediatric radiologist at 3 neonatal intensive care units in North Carolina, USA, between January 1998 and December 2004. NEC was confirmed using radiological and surgical pathology findings. Infants were assessed by 3 years using the Bayley Scales of Infant Development, second edition.

RESULTS

35 of 112 (31%) of study patients developed NEC. NEC was diagnosed subsequent to PVHI by a median of 16.6 days (95% CI [9.5, 24.9], p < 0.0001). Indomethacin use and the presence of bilateral PVHI were associated with an increased risk of subsequent NEC (OR 2.8, 95% CI [1.1, 7.2] and OR 2.4, 95% CI [1.1, 5.7], respectively). Having bilateral versus unilateral PVHI was associated with a 2.34-fold increased risk of death (95% CI [1.27, 4.33], p = 0.007). NEC was not associated with worse motor outcomes in this population. Overall, the probability of a mental development index >70 was greatest for infants with unilateral PVHI versus bilateral PVHI, although the presence of NEC was associated with worse cognitive outcomes in both groups.

CONCLUSIONS

Premature infants with PVHI often subsequently develop NEC, especially if they have bilateral PVHI and are exposed to indomethacin. While NEC results in worse neurodevelopmental outcomes, PVHI severity appears more important to the outcome of these infants.

Dilated intercellular space in chronic laryngitis and gastro-oesophageal reflux disease: at baseline and post-lansoprazole therapy

BACKGROUND

Dilation of intercellular spaces is reported to be an early morphological marker in gastro-oesophageal reflux. It remains unknown if this marker is useful in diagnosing reflux-related chronic laryngitis.

AIM

To determine histopathology and electron microscopic changes in oesophageal and laryngeal epithelium in chronic laryngitis.

METHODS

In this prospective blinded study, we enrolled 53 participants: 15 controls, 20 patients with GERD and 18 patients with chronic laryngitis. The latter two groups were subsequently treated with lansoprazole 30 mg bid for 12-weeks. Baseline and postacid suppressive therapy biopsies were obtained from distal oesophagus and laryngeal postcricoid areas. Biopsy specimens were evaluated for histopathology and dilated intercellular space changes.

RESULTS

There was no significant increase in oesophageal or laryngeal epithelium intercellular spaces among GERD or laryngitis patients compared with controls at baseline or postacid suppressive therapy. Only patients with GERD had significantly (P = 0.03) higher proportion of moderate-to-severe oesophageal spongiosis and basal cell hyperplasia, which normalized postacid suppressive therapy.

CONCLUSIONS

There was no increase in the width of intercellular spaces in the oesophagus or larynx in GERD or chronic laryngitis at baseline or postacid suppressive therapy. Our findings question the uniform presence of dilated intercellular space in patients with GERD.

Transnasal Esophagoscopy Findings: Interspecialty Comparison

Objective

Otolaryngologists implement transnasal esophagoscopy (TNE) to assess esophageal pathology. Previous studies using TNE to evaluate esophageal pathology have been limited in various ways. These are largely retrospective and deal with select patient populations. There are currently no data on the prevalence of esophageal pathology in “all comers” to an otolaryngology voice center. The objectives are to assess the prevalence of esophageal pathology in this population and determine the inter-observer variability of the findings reviewed by an otolaryngologist and a gastroenterologist.

Methods

Consecutive patients with throat symptoms presenting to the voice center were asked to undergo TNE. The findings were videotaped and reviewed by an otolaryngologist and a gastroesophagologist blinded to the patients’ presenting complaint.

Results

50 patients were selected prospectively to undergo TNE. Hoarseness was the most common presenting symptom (68%). According to the gastroesophagologist, the prevalence of esophageal findings was: Barrett's esophagus (12%), esophagitis (10%), hiatal hernia (32%), and esophageal stricture (10%). The percent agreement for a normal study was 72% (kappa 0.44). The percent agreement (kappa value) for various pathologic findings are as follows: Barrett's esophagus, 86% (0.45); esophagitis, 88% (0.43); hiatal hernia, 76% (0.39); and esophageal stricture, 96% (0.73). The frequency of an exact agreement between raters was 54%. For an abnormal study, the percent agreement was 80%. The reviewers were 7.11 times more likely to agree than disagree (p = 0.002).

Conclusions

Esophageal abnormalities are common in patients presenting to a voice subspecialty clinic. An interdisciplinary approach can provide this population with complementary patient care.

Intracellular distribution of amino acids in an slp1 vacuole-deficient mutant of the yeast Saccharomyces cerevisiae

Amino acid pools were compared in a constructed diploid strain of Saccharomyces cerevisiae, SKD1, and a closely related strain, SKD2, carrying the slp1 mutation characterized by low pools of lysine and lacking a central vacuole. Cells of SKD2 grew more poorly than SKD1 but took up the same total amount of amino acids from the medium per cell although the profile differed between the two strains. Initially, the total pool was much higher in SKD1 than in SKD2 but the overall relative distribution between cytosol and vacuole was identical and mainly cytosolic even though the composition differed between the two strains. At the end of growth the amino acid concentration had increased and become predominantly vacuolar. Two days later the total pool in SKD1 had declined to the starting level but the intracellular distribution remained identical to that at the end of fermentation. The total concentration of amino acids in SKD2 continued to increase, particularly in the cytosol.

Characteristics of maltose transporter activity in an ale and large strain of the yeast Saccharomyces cerevisiae

Kinetic studies on maltose uptake by ale and larger yeasts showed lower Km and higher Vmax values than for laboratory yeasts. Eadie-Hofstee plots were biphasic and inhibition by sulphydryl reagents was consistent with low affinity uptake by a specific transporter rather than by non-specific adsorption. High affinity maltose transport by both strains was inhibited by galactose, CCCP, 2, 4,-DNP and NEM. In contrast, glucose and pCMBS inhibited high affinity transport by the ale yeast but not by the larger yeast. In the case of pCMBS the difference could result from a single amino acid change in the maltose transporter.

Control of cell morphology of the yeast Saccharomyces cerevisiae by nutrient limitation in continuous culture

Saccharomyces cerevisiae IFO 0203, a polyploid yeast used in ethanol production in Japan, grows as ovoid cells in unstirred batch culture and on fully nutritive agar plates (2% w/v glucose; 0.67% w/v Difco yeast nitrogen base). Extensively branched pseudohyphae formed on 0.01% w/v ammonium sulphate plates within a few days. In continuous culture with high oxygen supply and limiting glucose, cells were elongated but growth was vigorous and the daughter cells separated well after budding. Limitation of growth by either nitrogen source or oxygen during continuous culture resulted in formation of truncated, occasionally branched, pseudohyphae up to five cells in length.

The influence of ammonium permease activity and carbon source on the uptake of ammonium from simple defined media by Saccharomyces cerevisiae

When growing under defined conditions, cells of the yeast Saccharomyces cerevisiae absorbed ammonium more rapidly with glucose as carbon source than with maltose. Ammonium pool sizes and permease activity were also higher in the glucose-grown cells and the relationship implies that firstly, the sugar is a primary determinant of ammonium permease activity and, secondly, the activity of the permease largely determines both the rate of ammonium uptake and ammonium pool size in the first part of the fermentation.

Asymmetric septal hypertrophy in patients on long-term hemodialysis

Echocardiographic studies were performed in 23 hypertensive patients who were receiving therapy with long-term hemodialysis. Five patients (22 percent) had normal thickness of the left ventricular wall. Eleven (48 percent) had symmetric left ventricular hypertrophy, and seven (30 percent) showed asymmetric septal hypertrophy, with a ratio of septal to posterior wall thickness of 1.3 or greater. The latter group differed from patients with hypertrophic cardiomyopathy in that patients on long-term hemodialysis had a dilated left ventricular dimension, a relatively normal diastolic slope of the mitral valve, absence of systolic motion of the mitral valve, and a septal to posterior wall ratio of less than 1.5. A high incidence of asymmetric septal hypertrophy in this and other studies indicates that this condition is not specific for hypertrophic cardiomyopathy. We suggest that in addition to asymmetric septal hypertrophy, the diagnosis of hypertrophic cardiomyopathy should be made in the light of the clinical picture, as well as other echocardiographic features.

Glutamate decarboxylase from barley embryos and roots. General properties and the occurrence of three enzymic forms

Glutamate decarboxylase in extracts of barley has a Km value for L-glutamate of 22 mM and is activated by the addition of pyridoxal phosphate by up to 3.5 times. Sucrose-density-gradient experiments indicate the presence of two enzyme forms with molecular weights 256000 and 120000. The lower-molecular-weight form appears to be relatively inactive and spontaneously associates to the higher-molecular-weight form on storage. The enzyme is inhibited by thiol reagents and the distribution of activity on density gradients is altered in favour of the lower-molecular-weight form by the presence of 2-mercaptoethanol. After removal of the 2-mercaptoethanol spontaneous association to the higher-molecular-weight form occurs. The presence of oxygen in the extraction buffer and in the water during imbibition leads to a relative increase in the higher-molecular-weight form compared with situations where oxygen is excluded. In contrast, glutamate decarboxylase in extracts of 3-day-old barley roots has a Km value for L-glutamate of 3.1 mM and is activated up to 10% by addition of pyridoxal phosphate. The root enzyme occurs as a single species with molecular weight 310000 and this is unaffected by 2-mercaptoethanol although thiol reagents do act as weak inhibitors. The molecular weight is also unaffected by the presence or absence of oxygen in the extraction buffers.

Inhibition of 3-phosphoglycerate dehydrogenase from Pisum sativum by purine nucleotides

The inhibition of 3-phosphoglycerate dehydrogenase from etiolated pea epicotyls by purine nucleoside di- and tri-phosphates is linear, competitive with regard to NADH, and the nucleotides are mutually exclusive in their binding. Free ATP and ADP are more effective inhibitors than are the respective magnesium complexes.

The isolation and characterization of 3-phosphoglycerate dehydrogenase from peas

1. 3-Phosphoglycerate dehydrogenase was purified 400-fold from crude extracts of etiolated pea epicotyls. 2. Michaelis constants were determined for all four substrates. 3. Loss of sensitivity to inhibition by l-serine occurs on purification. 4. The purified enzyme is inhibited by thiol-group reagents and, with N-ethyl-maleimide, protection is afforded by 3-phosphoglycerate though not by NAD(+).

Inhibition of 3-phosphoglycerate dehydrogenase by l-serine

1. l-Serine was shown to be a highly specific inhibitor of 3-phosphoglycerate dehydrogenase. 2. 3-Phosphoglycerate dehydrogenase is cold-labile with respect to its catalytic activity and to sensitivity to serine. 3. l-Serine protects the catalytic site as well as the inhibitor site. 4. Glycerol protects the catalytic site as well as the inhibitor site. 5. Serine acts as a ;classical' non-competitive inhibitor of fresh preparations of 3-phosphoglycerate dehydrogenase. 6. ;Aged' preparations when assayed at pH6.5 show sigmoid inhibition curves at saturating substrate concentrations. 7. A generalized model is advanced to account for the variation of the catalytic activity and the inhibitory effect of l-serine with time and conditions. 8. The possibility that the sigmoid kinetics of inhibition observed are an artifact of isolation is discussed.