Diagnostic accuracy of prenatal ultrasound in coarctation of aorta: systematic review and individual participant data meta-analysis.

OBJECTIVE: To determine the diagnostic accuracy of prenatal ultrasound in detecting coarctation of the aorta (CoA). METHODS: An individual participant data meta-analysis was performed to report on the strength of association and diagnostic accuracy of different ultrasound signs in detecting CoA prenatally. MEDLINE, EMBASE and CINAHL were searched for studies published between January 2000 and November 2021. Inclusion criteria were fetuses with suspected isolated CoA, defined as ventricular and/or great vessel disproportion with right dominance on ultrasound assessment. Individual participant-level data were obtained by two leading teams. PRISMA-IPD and PRISMA-DTA guidelines were used for extracting data, and the QUADAS-2 tool was used for assessing quality and applicability. The reference standard was CoA, defined as narrowing of the aortic arch, diagnosed after birth. The most commonly evaluated parameters on ultrasound, both in B-mode and on Doppler, constituted the index test. Summary estimates of sensitivity, specificity, diagnostic odds ratio (DOR) and likelihood ratios were computed using the hierarchical summary receiver-operating-characteristics model. RESULTS: The initial search yielded 72 studies, of which 25 met the inclusion criteria. Seventeen studies (640 fetuses) were included. On random-effects logistic regression analysis, tricuspid valve/mitral valve diameter ratio > 1.4 and > 1.6, aortic isthmus/arterial duct diameter ratio < 0.7, hypoplastic aortic arch (all P < 0.001), aortic isthmus diameter Z-score of < -2 in the sagittal (P = 0.003) and three-vessel-and-trachea (P < 0.001) views, pulmonary artery/ascending aorta diameter ratio > 1.4 (P = 0.048) and bidirectional flow at the foramen ovale (P = 0.012) were independently associated with CoA. Redundant foramen ovale was inversely associated with CoA (P = 0.037). Regarding diagnostic accuracy, tricuspid valve/mitral valve diameter ratio > 1.4 had a sensitivity of 72.6% (95% CI, 48.2-88.3%), specificity of 65.4% (95% CI, 46.9-80.2%) and DOR of 5.02 (95% CI, 1.82-13.9). The sensitivity and specificity values were, respectively, 75.0% (95% CI, 61.1-86.0%) and 39.7% (95% CI, 27.0-53.4%) for pulmonary artery/ascending aorta diameter ratio > 1.4, 47.8% (95% CI, 14.6-83.0%) and 87.6% (95% CI, 27.3-99.3%) for aortic isthmus diameter Z-score of < -2 in the sagittal view and 74.1% (95% CI, 58.0-85.6%) and 62.0% (95% CI, 41.6-78.9%) for aortic isthmus diameter Z-score of < -2 in the three-vessel-and-trachea view. Hypoplastic aortic arch had a sensitivity of 70.0% (95% CI, 42.0-88.6%), specificity of 91.3% (95% CI, 78.6-96.8%) and DOR of 24.9 (95% CI, 6.18-100). The diagnostic yield of prenatal ultrasound in detecting CoA did not change significantly when considering multiple categorical parameters. Five of the 11 evaluated continuous parameters were independently associated with CoA (all P < 0.001) but all had low-to-moderate diagnostic yield. CONCLUSIONS: Several prenatal ultrasound parameters are associated with an increased risk for postnatal CoA. However, diagnostic accuracy is only moderate, even when combinations of parameters are considered. © 2024 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Role of Doppler ultrasound at time of diagnosis of late-onset fetal growth restriction in predicting adverse perinatal outcome: prospective cohort study.

OBJECTIVE: Pregnancies complicated by late-onset fetal growth restriction (FGR) are at increased risk of short- and long-term morbidities. Despite this, identification of cases at higher risk of adverse perinatal outcome, at the time of FGR diagnosis, is challenging. The aims of this study were to elucidate the strength of association between fetoplacental Doppler indices at the time of diagnosis of late-onset FGR and adverse perinatal outcome, and to determine their predictive accuracy. METHODS: This was a prospective study of consecutive singleton pregnancies complicated by late-onset FGR. Late-onset FGR was defined as estimated fetal weight (EFW) or abdominal circumference (AC) < 3rd centile, or EFW or AC < 10th centile and umbilical artery (UA) pulsatility index (PI) > 95th centile or cerebroplacental ratio (CPR) < 5th centile, diagnosed after 32 weeks. EFW, uterine artery PI, UA-PI, fetal middle cerebral artery (MCA) PI, CPR and umbilical vein blood flow normalized for fetal abdominal circumference (UVBF/AC) were recorded at the time of the diagnosis of FGR. Doppler variables were expressed as Z-scores for gestational age. Composite adverse perinatal outcome was defined as the occurrence of at least one of emergency Cesarean section for fetal distress, 5-min Apgar score < 7, umbilical artery pH < 7.10 and neonatal admission to the special care unit. Logistic regression analysis was used to elucidate the strength of association between different ultrasound parameters and composite adverse perinatal outcome, and receiver-operating-characteristics (ROC)-curve analysis was used to determine their predictive accuracy. RESULTS: In total, 243 consecutive singleton pregnancies complicated by late-onset FGR were included. Composite adverse perinatal outcome occurred in 32.5% (95% CI, 26.7-38.8%) of cases. In pregnancies with composite adverse perinatal outcome, compared with those without, mean uterine artery PI Z-score (2.23 ± 1.34 vs 1.88 ± 0.89, P = 0.02) was higher, while Z-scores of UVBF/AC (-1.93 ± 0.88 vs -0.89 ± 0.94, P ≤ 0.0001), MCA-PI (-1.56 ± 0.93 vs -1.22 ± 0.84, P = 0.004) and CPR (-1.89 ± 1.12 vs -1.44 ± 1.02, P = 0.002) were lower. On multivariable logistic regression analysis, Z-scores of mean uterine artery PI (P = 0.04), CPR (P = 0.002) and UVBF/AC (P = 0.001) were associated independently with composite adverse perinatal outcome. UVBF/AC Z-score had an area under the ROC curve (AUC) of 0.723 (95% CI, 0.64-0.80) for composite adverse perinatal outcome, demonstrating better accuracy than that of mean uterine artery PI Z-score (AUC, 0.593; 95% CI, 0.50-0.69) and CPR Z-score (AUC, 0.615; 95% CI, 0.52-0.71). A multiparametric prediction model including Z-scores of MCA-PI, uterine artery PI and UVBF/AC had an AUC of 0.745 (95% CI, 0.66-0.83) for the prediction of composite adverse perinatal outcome. CONCLUSION: While CPR and uterine artery PI assessed at the time of diagnosis are associated independently with composite adverse perinatal outcome in pregnancies complicated by late-onset FGR, their diagnostic performance for composite adverse perinatal outcome is low. UVBF/AC showed better accuracy for prediction of composite adverse perinatal outcome, although its usefulness in clinical practice as a standalone predictor of adverse pregnancy outcome requires further research. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Papel de la ecografía Doppler en el momento del diagnóstico de la restricción del crecimiento fetal de aparición tardía para la predicción de resultados perinatales adversos: estudio prospectivo de cohortes OBJETIVO: Los embarazos complicados por la restricción del crecimiento fetal (RCF) de aparición tardía tienen un mayor riesgo de morbilidad a corto y largo plazo. A pesar de ello, es difícil identificar los casos con mayor riesgo de resultados perinatales adversos en el momento del diagnóstico de RCF. Los objetivos de este estudio fueron dilucidar la fortaleza de la asociación entre los índices Doppler fetoplacentarios en el momento del diagnóstico de la RCF de aparición tardía y el resultado perinatal adverso, y determinar su precisión predictiva. MÉTODOS: Este fue un estudio prospectivo de embarazos consecutivos con feto único complicados por una RCF de aparición tardía. La aparición tardía de la RCF se definió como peso estimado del feto (PEF) o circunferencia abdominal (CA) <3er percentil, o PEF o CA <10o percentil junto con índice de pulsatilidad (IP) de la arteria umbilical (AU) >95o percentil, o una relación cerebroplacentaria (RCP) <5o percentil, diagnosticado después de las 32 semanas. El PEF, el IP de la arteria uterina (IP-AU), el IP de la arteria cerebral media fetal (ACM), la RCP y el flujo sanguíneo de la vena umbilical normalizado para la circunferencia abdominal fetal (UVBF/AC, por sus siglas en inglés) se registraron en el momento del diagnóstico de RCF. Las variables Doppler se expresaron como puntuaciones Z para la edad gestacional. El resultado perinatal adverso compuesto se definió como la ocurrencia de al menos una cesárea de emergencia por sufrimiento fetal, test de Apgar a los 5 minutos <7, pH de la arteria umbilical <7,10 y el ingreso a la unidad de cuidados especiales de recién nacidos. Se utilizó el análisis de regresión logística para dilucidar la fortaleza de la asociación entre los diferentes parámetros de la ecografía y el resultado perinatal adverso compuesto, y se empleó el análisis de la curva de características operativas del receptor (ROC, por sus siglas en inglés) para determinar su precisión predictiva. RESULTADOS: En total, se incluyeron 243 embarazos con feto único consecutivos complicados por RCF de aparición tardía. El resultado perinatal adverso compuesto se produjo en el 32,5% (IC 95%, 26,7-38,8%) de los casos. En los embarazos con resultados perinatales adversos compuestos, en comparación con los que no los tuvieron, la puntuación Z del IP de la arteria uterina media (2,23±1,34 vs 1,88±0,89, P=0,02) fue mayor, mientras que las puntuaciones Z de UVBF/AC (-1,93±0,88 vs -0,89±0,94, P≤0,0001), IP-ACM (-1,56±0,93 vs -1,22±0,84, P=0,004) y RCP (-1,89±1,12 vs -1,44±1,02, P=0,002) fueron más bajas. En el análisis de regresión logística multivariable, las puntuaciones Z del IP de la arteria uterina media (P=0,04), RCP (P=0,002) y UVBF/AC (P=0,001) estuvieron asociadas de forma independiente con el resultado perinatal adverso compuesto. La puntuación Z del UVBF/AC tuvo un área bajo la curva (ABC) ROC de 0,723 (IC 95%, 0,64-0,80) para el resultado perinatal adverso compuesto, demostrando una mejor precisión que la de la puntuación Z del IP de la arteria uterina media (ABC, 0,593; IC 95%, 0,50-0,69) y la de la puntuación Z de la RCP (ABC, 0,615; IC 95%, 0,52-0,71). Un modelo de predicción multiparamétrico que incluía las puntuaciones Z del IP-ACM, el IP de la arteria uterina y el UVBF/AC resultó en un ABC de 0,745 (IC 95%, 0,66-0,83) para la predicción de un resultado perinatal adverso compuesto. CONCLUSIÓN: Aunque la RCP y el IP de la arteria uterina evaluados en el momento del diagnóstico están asociados de forma independiente con un resultado perinatal adverso compuesto en embarazos complicados por una RCF de aparición tardía, la eficacia del diagnóstico para el resultado perinatal adverso compuesto es baja. El UVBF/AC mostró una mayor precisión para la predicción de un resultado perinatal adverso compuesto, aunque su utilidad en la práctica clínica como parámetro indicativo independiente del resultado adverso del embarazo requiere más investigación. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Role of first-trimester umbilical vein blood flow in predicting large-for-gestational age at birth.

OBJECTIVES: To describe umbilical vein (UV) hemodynamics at 11 + 0 to 13 + 6 weeks of gestation in pregnancies delivering a large-for-gestational-age (LGA) neonate, and to build a multiparametric model, including pregnancy and ultrasound characteristics in the first trimester, that is able to predict LGA at birth. METHODS: This was a matched case-control study, of singleton pregnancies that underwent ultrasound examination at 11 + 0 to 13 + 6 weeks for aneuploidy screening, at a single center over a 4-year period. Cases were women who delivered a neonate with birth weight (BW) > 90th centile for gestational age and sex, according to local birth-weight standards, while controls were those who delivered a neonate with BW ranging between the 10th and 90th centiles, matched for maternal and gestational age, at a ratio of 1:3. Each included case underwent Doppler assessment of the uterine arteries and UV, including measurement of its diameter, time-averaged maximum velocity (TAMXV) and UV blood flow (UVBF). UVBF and its components were expressed as Z-scores. Fisher's exact test and Mann-Whitney U-test were used to compare differences in maternal biomarkers and ultrasound characteristics between pregnancies complicated by LGA and controls. Logistic regression and receiver-operating-characteristics (ROC) curve analyses were carried out to identify independent predictors of LGA and to build a multiparametric prediction model integrating different maternal, pregnancy and ultrasound characteristics. Subgroup analysis was also performed, considering women who delivered a neonate with BW > 4000 g. RESULTS: In total, 964 pregnancies (241 with LGA at birth and 723 without) were included in the study. In LGA pregnancies compared with controls, UV-TAMXV Z-score (0.8 (interquartile range (IQR), 0.4-1.5) vs 0.0 (IQR, -0.3 to 0.5); P ≤ 0.001) and UVBF Z-score (1.3 (IQR, 0.8-1.9) vs 0.1 (IQR, -0.4 to 0.4); P ≤ 0.001) were higher, while there was no difference in median UV diameter Z-score (P = 0.56). Median uterine artery pulsatility index multiples of the median (MoM; 0.94 (IQR, 0.78-1.12) vs 1.02 (IQR, 0.84-1.19); P = 0.04) was significantly lower in LGA pregnancies. On multivariate logistic regression analysis, maternal body mass index (BMI; adjusted odds ratio (aOR), 1.2 (95% CI, 1.1-1.7); P < 0.001), parity (aOR, 1.4 (95% CI, 1.2-1.6); P < 0.001), pregnancy-associated plasma protein-A (PAPP-A) MoM (aOR, 1.1 (95% CI, 1.0-1.6); P = 0.04) and UVBF Z-score (aOR, 1.6 (95% CI, 1.1-1.9); P < 0.001) were associated independently with LGA. A multiparametric model integrating parity, BMI and PAPP-A MoM provided an area under the ROC curve (AUC) of 0.72 (95% CI, 0.67-0.76) for the prediction of LGA. The addition of UVBF Z-score to this model significantly improved the prediction of LGA provided by maternal and biochemical factors, with an AUC of 0.79 (95% CI, 0.75-0.83; P = 0.03). Similarly, the model incorporating UVBF Z-score predicted BW > 4000 g with an AUC of 0.83 (95% CI, 0.75-0.93). CONCLUSIONS: UVBF measured at the time of the 11-14-week scan is associated independently with, and is predictive of, LGA and BW > 4000 g. Adding measurement of UVBF to a multiparametric model that includes maternal (parity and BMI) and biochemical (PAPP-A) parameters improves the diagnostic accuracy of prenatal screening for LGA at birth. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

New method to predict need for Rashkind procedure in fetuses with dextro-transposition of the great arteries.

OBJECTIVE: Prenatal congenital heart disease classification systems distinguish between critical dextro-transposition of the great arteries (d-TGA) with restriction of the foramen ovale (FO) (which requires a Rashkind procedure within the first 24 h following delivery) and d-TGA for which surgery is planned (after prostaglandin perfusion or Rashkind procedure later than 24 h after delivery). However, current prenatal diagnostic criteria for postnatal FO restriction in d-TGA are inadequate, resulting in a high false-negative rate. We aimed to identify echocardiographic features to predict the urgent need for Rashkind procedure. METHODS: We identified retrospectively 98 patients with singleton pregnancy diagnosed prenatally with fetal d-TGA at two European centers from 2006 to 2013. Two groups were compared: (1) those in whom the Rashkind procedure was performed within the first 24 h postnatally; and (2) those who did not undergo a Rashkind procedure before cardiac surgery. Exclusion criteria were: (1) no fetal echocardiography within 3 weeks prior to delivery (n = 18); (2) delivery before 37 weeks of gestation (n = 6); (3) improper or lack of measurement of pulmonary vein maximum flow velocity (n = 10); (4) lack of neonatal follow-up data (n = 9); (5) Rashkind procedure performed more than 24 h after delivery (n = 4). RESULTS: Fifty-one patients met the inclusion criteria: 29 who underwent the Rashkind procedure and 22 who did not. There were no differences between these two study groups in terms of maternal age, gestational age at time of fetal echocardiography, fetal biometric measurements, estimated fetal weight, rate of Cesarean delivery, newborn weight or Apgar score at 1 min. There were also no differences during prenatal life between the two groups in terms of fetal cardiac size (heart area/chest area ratio), rate of disproportion between left and right ventricle, FO diameter and maximum velocity of flow through the FO. However, the pulmonary vein maximum velocity was significantly higher in the group requiring a Rashkind procedure (47.62 ± 7.48 vs 32.21 ± 5.47 cm/s; P < 0.001). The cut-off value of 41 cm/s provided maximum specificity (100%) and positive predictive value (100%) at only a slight cost of sensitivity (82%) and NPV (86%). The prenatal appearance of the FO also differed between the groups, the FO valve being flat in 52% of those requiring a Rashkind procedure. CONCLUSIONS: In fetuses with d-TGA, prenatal sonographic findings of increased pulmonary venous blood flow and flattened FO valve were associated with the need for a Rashkind procedure within the first 24 h postnatally; these echocardiographic features could be used to predict prenatally a need for the procedure following delivery. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Predicted and unpredicted cross-reactions of an acetylphosphogalactan of Sporobolomyces yeast.

The teichoic acid of streptococcal Group N, with end groups of galactose phosphate, had been shown to cross-react with antipneumococcal sera of types VI, XIV, XVI, and XXVII. End groups of D-galactose-1-phosphate in the phosphogalactans of Sporobolomyces yeasts made it predictable that these galactans would precipitate the same antipneumococcal sera and also antisera to streptococcal Group N. The predictions were verified, and other unpredicted reactions were found. Precipitation of much of the antibody in an antipneumoccal type XVIII horse serum was shown to be due to O-acetyl-D-galactose residues in the phosphogalactan, in accord with earlier information that an O-acetyl sugar was a principal determinant of S XVIII. The new results identify this sugar as D-galactose. Since it is linked 1,3- in S XVIII, the O-acetyl group in the Sporobolomyces galactan is probably also on a 1,3-linked residue. Another major cross-reaction in anti-S. paratyphi A serum characterizes the galactose residues in the "O" polysaccharide of the bacillus as members of the D-series probably linked in tandem 1,6-, 1,6-; 1,6-, 1,3-; 1,3-, 1,6-; or 1,3-, 1,3-. Reactions of periodate-oxidized-reduced products confirm the conclusions stated above. Quantitative data are given.

Fetal cardiology: changing the definition of critical heart disease in the newborn.

Infants born with congenital heart disease (CHD) may require emergent treatment in the newborn period. These infants are likely to benefit the most from a prenatal diagnosis, which allows for optimal perinatal planning. Several cardiac centers have created guidelines for the management of these high-risk patients with CHD. This paper will review and compare several prenatal CHD classification systems with a particular focus on the most critical forms of CHD in the fetus and newborn. A contemporary definition of critical CHD is one which requires urgent intervention in the first 24 h of life to prevent death. Such cardiac interventions may be not only life saving for the infant but also decrease subsequent morbidity. Critical CHD cases may require delivery at specialized centers that can provide perinatal, obstetric, cardiology and cardiothoracic surgery care. Fetuses diagnosed in mid-gestation require detailed fetal diagnostics and serial monitoring during the prenatal period, in order to assess for ongoing changes and identify progression to a more severe cardiac status. Critical CHD may progress in utero and there is still much to be learned about how to best predict those who will require urgent neonatal interventions. Despite improved therapeutic capabilities, newborns with critical CHD continue to have significant morbidity and mortality due to compromise that begins in the delivery room. Fetal echocardiography is the best way to predict the need for specialized care at birth to improve outcome. Once the diagnosis is made of critical CHD, delivery at the proper time and in appropriate institution with specific care protocols should be initiated. More work needs to be done to better delineate the risk factors for progression of critical CHD and to determine which newborns will require specialized care. The most frequently described forms of critical CHD requiring immediate intervention include hypoplastic left heart syndrome with intact or severely restricted atrial septum, obstructed total anomalous pulmonary venous return and transposition of the great arteries with restrictive atrial septum.

Type-specific polysaccharides of Cryptococcus neoformans. n.m.r.-spectral study of a glucuronomannan chemically derived from a Tremella mesenterica exopolysaccharide.

A glucuronomannan (GM) was derived by removal, through Smith degradation, of xylose from the native (3-O-acetylglucurono)xylomannan exopolysaccharide isolated from Tremella mesenterica. 13C-N.m.r. chemical shifts measured at various pD values were compared for p-nitrophenyl beta-D-glucopyranosiduronic acid (1) and two GMs (2 and 3) differing in GlcA content (Man:GlcA; 2, 10:1; and 3, 5:1). Also measured and compared were pKa values for 1 and 2. One-dimensional and two-dimensional (COSY and HETCOR) n.m.r. data allowed unambiguous assignments of pD-sensitive chemical shifts due to 2-O-beta-D-GlcpA substituents attached to a (1----3)-linked alpha-D-Manp backbone. The pKa and n.m.r. data indicated that the CO2H groups in either GM are independent of each other, and are similar in behavior to those of p-nitrophenyl beta-D-glucopyranosiduronic acid molecules. The n.m.r. data confirmed the previous, chemically deduced, structural role of GlcpA in the native polysaccharide from T. mesenterica, and indicated that significant pD-induced changes occur in the stabilities of the glycosidic orientations in the GM. Previous 13C-n.m.r. assignments for 2-O-beta-D-GlcpA in polysaccharides derived from Cryptococcus neoformans serotype A-variant were confirmed, except for the signal due to the anomeric carbon atom. This signal is now known to be pD-sensitive. In acidic solutions, it is coincident with the signal (104.5 p.p.m.) due to the anomeric carbon atoms of the unsubstituted alpha-D-Manp backbone residues. In basic solutions, the 2-O-beta-D-GlcpA anomeric carbon resonance is shifted upfield by approximately 0.2 p.p.m., and is observed as a separate signal.

Phosphorus-31 nuclear magnetic resonance spectroscopy of extracellular, yeast O-phosphonohexoglycans.

P nuclear magnetic resonance spectra of a number of purified yeast O-phosphonohexoglycans were recorded. The data therefrom were correlated with established chemicals aspects of individual and collective polymer structures, permitting (a) conclusions to be drawn regarding the chemical environment of the phosphate groups of these polymers, and (b) assignment of anormeric configurations to the hexosyl phosphate residues.

Influence of the culture medium on the synthesis of alpha-D-glucans by Streptococcus cricetus AHT.

Three different alpha-D-glucosyltransferases (GTFs) were separated from culture filtrates of Streptococcus cricetus strain AHT grown in a complex, standard medium in batch culture or under defined conditions of growth in the chemostat. Two of the enzymes (GTF-S1 and GTF-S2) converted sucrose into branched, soluble dextrans, and the third (GTF-I) produced a relatively linear, water-insoluble, predominantly (1----3)-linked alpha-D-glucan. When the organism was grown in complex medium modified by the removal of the fraction of high molecular weight, only GTF-S1 and GTF-S2 were released, and no GTF-I was detected. The water-insoluble glucan fraction obtained by incubating the cell-free filtrate with sucrose contained from 17 to 25% of (1----3)-glucosidic linkages, and accounted for up to 78 and 4% of the total glucans derived from growth in standard and modified medium, respectively. The soluble glucans produced in the same reaction were fractionated with ethanol to give, from both media, two distinct dextrans comprising (1) a highly branched dextran similar to the S1-dextran product of GTF-S1 and (2) a dextran containing fewer branch linkages and up to 86% of (1----6)-alpha-D-glucosidic linkages. A GTF responsible for the synthesis of the latter dextran was not separated. The structures of the glucan fractions and the products of the separated GTF were examined by enzymic degradation and methylation analysis.

Methylation and acetolysis of extracellular D-mannans from yeast.

Methylation-fragmentation analyses were conducted on a series of extra-cellular, yeast alpha-D-linked mannans representing six different structural types. D-Mannans of low degree of branching were produced by Hansenula capsulata strains and by species related to H. holstii, The former consisted primarily of (1 leads to 2)- and (1 leads to 6)-linked D-mannosyl residues; the latter, of (1 leads to 2)- and (1 leads to 3)-linked D-mannosyl residues. Although the remaining structural types were highly branched, each gave distinct methylation-patterns indicative of (1 leads to 6)-linked backbones to which are appended non-(1 leads to 6)-linked side-chains. Acetolysis studies were correlated with the methylation analyses, and the correlation demonstrated that each branched polymer possesses side chains of heterogeneous length.

Growth-related substituent changes in exopolysaccharides of fast-growing rhizobia.

Pyruvic acid and O-acetyl groups are the major noncarbohydrate substituents in exopolysaccharides (EPS) produced by fast-growing species of Rhizobium. EPS substituent variations were observed among strains of the same species. The amounts of these substituents also varied with culture age; pyruvic acid increased in the EPS of all four species, whereas O-acetyl increased in Rhizobium trifolii and R. leguminosarum EPS, decreased in R. meliloti EPS, and remained constant in R. phaseoli EPS. The use of glycerol as a substrate for R. meliloti significantly increased EPS yields, whereas mannitol increased those of the other three Rhizobium species.

Effect of Ultraviolet-B (280 to 320 nm) Radiation on Blue-Green Algae (Cyanobacteria), Possible Biological Indicators of Stratospheric Ozone Depletion.

The effect of ultraviolet-B (280 to 320 nm) irradiation on physiological activities of Anabaena flos-aquae and the water fern Azolla caroliniana has been studied under conditions where lethal effects of irradiation are absent. Nitrogenase activity, measured as acetylene reduction, specifically declined during irradiation with low levels of ultraviolet-B, whereas other physiological activities were unaffected. These findings indicate that measurement of acetylene reduction by cyanobacteria may serve as a specific, sensitive biochemical assay to assess environmental ultraviolet-B effects due to depletion of stratospheric ozone.

Specificity of acceptor binding to Leuconostoc mesenteroides B-512F dextransucrase: binding and acceptor-product structure of alpha-methyl-D-glucopyranoside analogs modified at C-2, C-3, and C-4 by inversion of the hydroxyl and by replacement of the hydroxyl with hydrogen.

The specificity of acceptor binding to the active site of dextransucrase was studied by using alpha-methyl-D-glucopyranoside analogs modified at C-2, C-3, and C-4 positions by (a) inversion of the hydroxyl group and (b) replacement of the hydroxyl group with hydrogen. 2-Deoxy-alpha-methyl-D-glucopyranoside was synthesized from 2-deoxyglucose; 3- and 4-deoxy-alpha-methyl-D-glucopyranosides were synthesized from alpha-methyl-D-glucopyranoside; and alpha-methyl-D-allopyranoside was synthesized from D-glucose. The analogs were incubated with [14C]sucrose and dextransucrase, and the products were separated by thin-layer chromatography and quantitated by liquid scintillation spectrometry. Structures of the acceptor products were determined by methylation analyses and optical rotation. The relative effectiveness of the acceptor analogs in decreasing order were 2-deoxy, 2-inverted, 3-deoxy, 3-inverted, 4-inverted, and 4-deoxy. The enzyme transfers D-glucopyranose to the C-6 hydroxyl of analogs modified at C-2 and C-3, to the C-4 hydroxyl of 4-inverted, and to the C-3 hydroxyl of 4-deoxy analogs of alpha-methyl-D-glucopyranoside. The data indicate that the hydroxyl group at C-2 is not as important for acceptor binding as the hydroxyl groups at C-3 and C-4. The hydroxyl group at C-4 is particularly important as it determines the binding orientation of the alpha-methyl-D-glucopyranoside ring.