The Application of HPLC-FLD and NMR in the Monitoring of Therapy Efficacy in Alpha-Mannosidosis.

BACKGROUND: Alpha-mannosidosis is a rare lysosomal storage disorder, caused by decreased activity of α-D-mannosidase. This enzyme is involved in the hydrolysis of mannosidic linkages in N-linked oligosaccharides. Due to the mannosidase defect, undigested mannose-rich oligosaccharides (Man2GlcNAc - Man9GlcNAc) accumulating in cells are excreted in large quantities in urine. METHODS: In this work, we determined the levels of urinary mannose-rich oligosaccharides in a patient subjected to novel enzyme replacement therapy. Urinary oligosaccharides were extracted using solid phase extraction (SPE), labeled by fluorescent tag 2-aminobenzamide, and quantified by high-performance liquid chromatography (HPLC) with fluorescence detector (FLD). The identity of peaks was determined by matrix-assisted laser desorption/ionization time-of-flight/time-of-flight (MALDI-TOF/TOF) mass spectrometry. In addition, the levels of urinary mannose-rich oligosaccharides were also quantified by 1H nuclear magnetic resonance (NMR) spectroscopy. The data were analyzed using one-tailed paired t-test and Pearson's correlation tests. RESULTS: Compared to levels before the administration of therapy, an approximately two-folds decrease in total mannose-rich oligosaccharides after one month of treatment was observed by NMR and HPLC. After four months, an approximately ten-folds significant decrease in total urinary mannose-rich oligosaccharides was detected, suggesting therapy effectiveness. A significant decrease in the levels of oligosaccharides with 7-9 mannose units was detected by HPLC. CONCLUSIONS: The application of both HPLC-FLD and NMR in quantification of oligosaccharide biomarkers is a suitable approach for monitoring of therapy efficacy in alpha-mannosidosis patients.

N-Glycoprofiling of SLC35A2-CDG: Patient with a Novel Hemizygous Variant.

Congenital disorders of glycosylation (CDG) are a group of rare inherited metabolic disorders caused by a defect in the process of protein glycosylation. In this work, we present a comprehensive glycoprofile analysis of a male patient with a novel missense variant in the SLC35A2 gene, coding a galactose transporter that translocates UDP-galactose from the cytosol to the lumen of the endoplasmic reticulum and Golgi apparatus. Isoelectric focusing of serum transferrin, which resulted in a CDG type II pattern, was followed by structural analysis of transferrin and serum N-glycans, as well as the analysis of apolipoprotein CIII O-glycans by mass spectrometry. An abnormal serum N-glycoprofile with significantly increased levels of agalactosylated (Hex3HexNAc4-5 and Hex3HexNAc5Fuc1) and monogalactosylated (Hex4HexNAc4 ± NeuAc1) N-glycans was observed. Additionally, whole exome sequencing and Sanger sequencing revealed de novo hemizygous c.461T > C (p.Leu154Pro) mutation in the SLC35A2 gene. Based on the combination of biochemical, analytical, and genomic approaches, the set of distinctive N-glycan biomarkers was characterized. Potentially, the set of identified aberrant N-glycans can be specific for other variants causing SLC35A2-CDG and can distinguish this disorder from the other CDGs or other defects in the galactose metabolism.

Comparison of CNN-Learned vs. Handcrafted Features for Detection of Parkinson's Disease Dysgraphia in a Multilingual Dataset.

Parkinson's disease dysgraphia (PDYS), one of the earliest signs of Parkinson's disease (PD), has been researched as a promising biomarker of PD and as the target of a noninvasive and inexpensive approach to monitoring the progress of the disease. However, although several approaches to supportive PDYS diagnosis have been proposed (mainly based on handcrafted features (HF) extracted from online handwriting or the utilization of deep neural networks), it remains unclear which approach provides the highest discrimination power and how these approaches can be transferred between different datasets and languages. This study aims to compare classification performance based on two types of features: features automatically extracted by a pretrained convolutional neural network (CNN) and HF designed by human experts. Both approaches are evaluated on a multilingual dataset collected from 143 PD patients and 151 healthy controls in the Czech Republic, United States, Colombia, and Hungary. The subjects performed the spiral drawing task (SDT; a language-independent task) and the sentence writing task (SWT; a language-dependent task). Models based on logistic regression and gradient boosting were trained in several scenarios, specifically single language (SL), leave one language out (LOLO), and all languages combined (ALC). We found that the HF slightly outperformed the CNN-extracted features in all considered evaluation scenarios for the SWT. In detail, the following balanced accuracy (BACC) scores were achieved: SL-0.65 (HF), 0.58 (CNN); LOLO-0.65 (HF), 0.57 (CNN); and ALC-0.69 (HF), 0.66 (CNN). However, in the case of the SDT, features extracted by a CNN provided competitive results: SL-0.66 (HF), 0.62 (CNN); LOLO-0.56 (HF), 0.54 (CNN); and ALC-0.60 (HF), 0.60 (CNN). In summary, regarding the SWT, the HF outperformed the CNN-extracted features over 6% (mean BACC of 0.66 for HF, and 0.60 for CNN). In the case of the SDT, both feature sets provided almost identical classification performance (mean BACC of 0.60 for HF, and 0.58 for CNN).

A novel homozygous mutation in the human ALG12 gene results in an aberrant profile of oligomannose N-glycans in patient's serum.

Congenital disorder of glycosylation type Ig (ALG12-CDG) is a rare inherited metabolic disease caused by a defect in alpha-mannosyltransferase 8, encoded by the ALG12 gene (22q13.33). To date, only 15 patients have been diagnosed with ALG12-CDG globally. Due to a newborn Slovak patient's clinical and biochemical abnormalities, the isoelectric focusing of transferrin was performed with observed significant hypoglycosylation typical of CDG I. Furthermore, analysis of neutral serum N-glycans by mass spectrometry revealed the accumulation of GlcNAc2Man5-7 and decreased levels of GlcNAc2Man8-9, which indicated impaired ALG12 enzymatic activity. Genetic analysis of the coding regions of the ALG12 gene of the patient revealed a novel homozygous substitution mutation c.1439T>C p.(Leu480Pro) within Exon 10. Furthermore, both of the patient's parents and his twin sister were asymptomatic heterozygous carriers of the variant. This comprehensive genomic and glycomic approach led to the confirmation of the ALG12 pathogenic variant responsible for the clinical manifestation of the disorder in the patient described.

Articulatory network reorganization in Parkinson's disease as assessed by multimodal MRI and acoustic measures.

INTRODUCTION: Hypokinetic dysarthria (HD) is common in Parkinson's disease (PD). Our objective was to evaluate articulatory networks and their reorganization due to PD pathology in individuals without overt speech impairment using a multimodal MRI protocol and acoustic analysis of speech. METHODS: A total of 34 PD patients with no subjective HD complaints and 25 age-matched healthy controls (HC) underwent speech task recordings, structural MRI, and reading task-induced and resting-state fMRI. Grey matter probability maps, task-induced activations, and resting-state functional connectivity within the regions engaged in speech production (ROIs) were assessed and compared between groups. Correlation with acoustic parameters was also performed. RESULTS: PD patients as compared Tto HC displayed temporal decreases in speech loudness which were related to BOLD signal increases in the right-sided regions of the dorsal language pathway/articulatory network. Among those regions, activation of the right anterior cingulate was increased in PD as compared to HC. We also found bilateral posterior superior temporal gyrus (STG) GM loss in PD as compared to HC that was strongly associated with diadochokinetic (DDK) irregularity in the PD group. Task-induced activations of the left STG were increased in PD as compared to HC and were related to the DDK rate control. CONCLUSIONS: The results provide insight into the neural correlates of speech production control and distinct articulatory network reorganization in PD apparent already in patients without subjective speech impairment.

Non-invasive stimulation of the auditory feedback area for improved articulation in Parkinson's disease.

INTRODUCTION: Hypokinetic dysarthria (HD) is a common symptom of Parkinson's disease (PD) which does not respond well to PD treatments. We investigated acute effects of repetitive transcranial magnetic stimulation (rTMS) of the motor and auditory feedback area on HD in PD using acoustic analysis of speech. METHODS: We used 10 Hz and 1 Hz stimulation protocols and applied rTMS over the left orofacial primary motor area, the right superior temporal gyrus (STG), and over the vertex (a control stimulation site) in 16 PD patients with HD. A cross-over design was used. Stimulation sites and protocols were randomised across subjects and sessions. Acoustic analysis of a sentence reading task performed inside the MR scanner was used to evaluate rTMS-induced effects on motor speech. Acute fMRI changes due to rTMS were also analysed. RESULTS: The 1 Hz STG stimulation produced significant increases of the relative standard deviation of the 2nd formant (p = 0.019), i.e. an acoustic parameter describing the tongue and jaw movements. The effects were superior to the control site stimulation and were accompanied by increased resting state functional connectivity between the stimulated region and the right parahippocampal gyrus. The rTMS-induced acoustic changes were correlated with the reading task-related BOLD signal increases of the stimulated area (R = 0.654, p = 0.029). CONCLUSION: Our results demonstrate for the first time that low-frequency stimulation of the temporal auditory feedback area may improve articulation in PD and enhance functional connectivity between the STG and the cortical region involved in an overt speech control.

The usefulness of determination of the procalcitonin (PCT) concentration in GBS piositive pregnant womens blood serum for anticipations of infections in newborns

Group-B streptococci (GBS) are commensal bacteria of the human body. They may, however, pose a serious life hazard to pregnant women. During labour, newborns of GBS-positive mothers run the risk of infections that may eventually lead to severe complications, sepsis or even death. For this reason, it is very important to find new diagnostic markers that will enable fast and effective diagnostics and control of the disease process. The level of procalcitonin emerges as a promising diagnostic parameter. AIM. Analysis of the impact of the procalcitonin (PCT) level in GBS-positive pregnant women on the possibility of complications and infections in mothers and newborns MATERIAL AND METHODS. The study group consisted of 115 GBS-positive pregnant women. For each mother-to-be, the CRP and the PCT concentration levels were determined. The clinical state of 117 newborns (2 twin pregnancies) was also assessed. After delivery, the CRP concentration level was determined in the newborns. The examinations had a retrospective character. RESULTS. 30 women showed a raised concentration of CRP and 13 ­ of PCT. No correlation was found between the two diagnostic markers. Similarly, no relation was found between a raised concentration of PCT and the occurrence of a bacterial infection or other complications in the parturient. A raised concentration of procalcitonin in the mother did not translate into the development of an infection in the newborn, either. CONCLUSIONS. The results of the study indicate that there is no correlation between a raised concentration of PCT in GBS-positive pregnant women and a raised CRP level. Abnormal PCT levels in the women covered by the study did not involve a higher frequency of the occurrence of complications or bacterial infections either in the mothers or in the newborns.

Quantitative Analysis of Relationship Between Hypokinetic Dysarthria and the Freezing of Gait in Parkinson's Disease.

Hypokinetic dysarthria (HD) and freezing of gait (FOG) are both axial symptoms that occur in patients with Parkinson's disease (PD). It is assumed they have some common pathophysiological mechanisms and therefore that speech disorders in PD can predict FOG deficits within the horizon of some years. The aim of this study is to employ a complex quantitative analysis of the phonation, articulation and prosody in PD patients in order to identify the relationship between HD and FOG, and establish a mathematical model that would predict FOG deficits using acoustic analysis at baseline. We enrolled 75 PD patients who were assessed by 6 clinical scales including the Freezing of Gait Questionnaire (FOG-Q). We subsequently extracted 19 acoustic measures quantifying speech disorders in the fields of phonation, articulation and prosody. To identify the relationship between HD and FOG, we performed a partial correlation analysis. Finally, based on the selected acoustic measures, we trained regression models to predict the change in FOG during a 2-year follow-up. We identified significant correlations between FOG-Q scores and the acoustic measures based on formant frequencies (quantifying the movement of the tongue and jaw) and speech rate. Using the regression models, we were able to predict a change in particular FOG-Q scores with an error of between 7.4 and 17.0 %. This study is suggesting that FOG in patients with PD is mainly linked to improper articulation, a disturbed speech rate and to intelligibility. We have also proved that the acoustic analysis of HD at the baseline can be used as a predictor of the FOG deficit during 2 years of follow-up. This knowledge enables researchers to introduce new cognitive systems that predict gait difficulties in PD patients.

Sweet characterisation of prostate specific antigen using electrochemical lectin-based immunosensor assay and MALDI TOF/TOF analysis: Focus on sialic acid.

The construction of a sensitive electrochemical lectin-based immunosensor for detection of a prostate specific antigen (PSA) is shown here. Three lectins with different carbohydrate specificities were used in this study to glycoprofile PSA, which is the most common biomarker for prostate cancer (PCa) diagnosis. The biosensor showed presence of α-L-fucose and α-(2,6)-linked terminal sialic acid within PSA´s glycan with high abundance, while only traces of α-(2,3)-linked terminal sialic acid were found. MALDI TOF/TOF mass spectrometry was applied to validate results obtained by the biosensor with a focus on determination of a type of sialic acid linkage by two methods. The first direct comparison of electrochemical immunosensor assay employing lectins for PSA glycoprofiling with mass spectrometric techniques is provided here and both methods show significant agreement. Thus, electrochemical lectin-based immunosensor has potential to be applied for prostate cancer diagnosis.

Characterisation of class I and II α-mannosidases from Drosophila melanogaster.

Homology searches indicated that up to five class I α-mannosidases (glycohydrolase family 47) and eight class II α-mannosidases (glycohydrolase family 38) are encoded by the fruitfly (Drosophila melanogaster) genome. Selected example mannosidases were expressed in secreted form using the yeast Pichia pastoris. A number of characteristics of these enzymes were determined with p-nitrophenyl-α-mannoside as substrate; particularly striking were the low optima (pH 5) of three class II mannosidases most closely related to known lysosomal mannosidases and the distinct Co(II)-requirement of a mannosidase previously named ManIIb. Some of the recombinant mannosidases were demonstrably active towards oligomannosidic glycans, specifically, the Co(II)-requiring ManIIb, two 'acidic' mannosidases and the class I mas-1 mannosidase. Other than previous characterisations of the well-known Golgi mannosidase II, this is the first study summarising various properties of recombinant mannosidases from the fruitfly.

Distantly related plant and nematode core α1,3-fucosyltransferases display similar trends in structure-function relationships.

Here, we present a comparative structure-function study of a nematode and a plant core α1,3-fucosyltransferase based on deletion and point mutations of the coding regions of Caenorhabditis elegans FUT-1 and Arabidopsis thaliana FucTA (FUT11). In particular, our results reveal a novel "first cluster motif" shared by both core and Lewis-type α1,3-fucosyltransferases of the GT10 family. To evaluate the role of the conserved serine within this motif, this residue was replaced with alanine in FucTA (S218) and FUT-1 (S243). The S218A replacement completely abolished the enzyme activity of FucTA, while the S243A mutant of FUT-1 retained 20% of the "wild-type" activity. Based on the results of homology modeling of FucTA, other residues potentially involved in the donor substrate binding were examined, and mutations of N219 and R226 dramatically affected enzymatic activity. Finally, as both FucTA and FUT-1 were shown to be N-glycosylated, we examined the putative N-glycosylation sites. While alanine replacements at single potential N-glycosylation sites of FucTA resulted in a loss of up to 80% of the activity, a triple glycosylation site mutant still retained 5%, as compared to the control. In summary, our data indicate similar trends in structure-function relationships of distantly related enzymes which perform similar biochemical reactions and form the basis for future work aimed at understanding the structure of α1,3-fucosyltransferases in general.

α-D-mannose derivatives as models designed for selective inhibition of Golgi α-mannosidase II.

Human Golgi α-mannosidase II (hGM) is a pharmaceutical target for the design of inhibitors with anti-tumor activity. Nanomolar inhibitors of hGM exhibit unwanted co-inhibition of the human lysosomal α-mannosidase (hLM). Hence, improving specificity of the inhibitors directed toward hGM is desired in order to use them in cancer chemotherapy. We report on the rapid synthesis of D-mannose derivatives having one of the RS-, R(SO)- or R(SO(2))- groups at the α-anomeric position. Inhibitory properties of thirteen synthesized α-D-mannopyranosides were tested against the recombinant enzyme Drosophila melanogaster homolog of hGM (dGMIIb) and hLM (dLM408). Derivatives with the sulfonyl [R(SO(2))-] group exhibited inhibitory activities at the mM level toward both dGMIIb (IC(50) = 1.5-2.5 mM) and dLM408 (IC(50) = 1.0-2.0 mM). Among synthesized, only the benzylsulfonyl derivative showed selectivity toward dGMIIb. Its inhibitory activity was explained based on structural analysis of the built 3-D complexes of the enzyme with the docked compounds.

Molecular characterization of 22 novel UDP-N-acetylglucosamine-1-phosphate transferase alpha- and beta-subunit (GNPTAB) gene mutations causing mucolipidosis types IIalpha/beta and IIIalpha/beta in 46 patients.

Mutational analysis of the GNPTAB gene was performed in 46 apparently unrelated patients with mucolipidosis IIalpha/beta or IIIalpha/beta, characterized by the mistargeting of multiple lysosomal enzymes as a consequence of a UDP-GlcNAc-1-phosphotransferase defect. The GNPTAB mutational spectrum comprised 25 distinct mutant alleles, 22 of which were novel, including 3 nonsense mutations (p.Q314X, p.R375X, p.Q507X), 5 missense mutations (p.I403T, p.C442Y, p.C461G, p.Q926P, p.L1001P), 6 microduplications (c.749dupA, c.857dupA, c.1191_1194dupGCTG, c.1206dupT, c.1331dupG, c.2220_2221dupGA) and 8 microdeletions (c.755_759delCCTCT, c.1399delG, c.1959_1962delTAGT, c.1965delC, c.2550_2554delGAAAA, c.3443_3446delTTTG, c.3487_3490delACAG, c.3523_3529delATGTTCC). All micro-duplications/deletions were predicted to result in the premature termination of translation. A novel exonic SNP (c.303G>A; E101E) was identified which is predicted to create an SFRS1 (SF2/ASF) binding site that may be of potential functional/clinical relevance. This study of mutations in the GNPTAB gene, the largest yet reported, extends our knowledge of the mutational heterogeneity evident in MLIIalpha/beta/MLIIIalpha/beta.

[Genital warts associated with HPV infection during II and III trimester of pregnancy--a case report and analysis of treatment options]. / Klykciny konczyste u ciezarnej w II i III trymestrze ciazy--opis sytuacji klinicznej i analiza zastosowanego leczenia.

More than 30 HPV types can infect the genital tract. Viral infection can be present in clinical, subclinical or latent form. A visible genital form of HPV infection are genital warts, which are commonly caused by HPV types 6 and 11, and appear on the vulva, cervix, vagina, urethra and anus. Oncogenic HPV types 16, 18, 31, 33 and 35 are also found in genital warts and are associated with vulval (VII), cervical (CIN) and anal (AIN) intraepithelial neoplasia. The general prevalence of HPV infection in the form of visible genital warts estimates to about 1% of sexually active adults. Approximately 15% of the infected group / of all adults have a subclinical or latent infection and at least 80% had been infected with one or more genital HPV types at some point in their lives. The highest rate of frequency of infections occurs in the group of adults, aged from 18 to 28. Over the last twenty years figures have shown a constant growth of the infection rate, which also includes pregnant women. Genital warts can proliferate during pregnancy due to altered immunity and increased blood supply. Cryotherapy, electrocautery, laser therapy, surgery or trichloroacetic acid may be used to remove the warts. In the paper a case report on genital warts associated with HPV infection during II and III trimester of pregnancy and analysis of treatment options has been presented.

Arabidopsis thaliana beta1,2-xylosyltransferase: an unusual glycosyltransferase with the potential to act at multiple stages of the plant N-glycosylation pathway.

XylT (beta1,2-xylosyltransferase) is a unique Golgi-bound glycosyltransferase that is involved in the biosynthesis of glycoprotein-bound N-glycans in plants. To delineate the catalytic domain of XylT, a series of N-terminal deletion mutants was heterologously expressed in insect cells. Whereas the first 54 residues could be deleted without affecting the catalytic activity of the enzyme, removal of an additional five amino acids led to the formation of an inactive protein. Characterization of the N-glycosylation status of recombinant XylT revealed that all three potential N-glycosylation sites of the protein are occupied by N-linked oligosaccharides. However, an unglycosylated version of the enzyme displayed substantial catalytic activity, demonstrating that N-glycosylation is not essential for proper folding of XylT. In contrast with most other glycosyltransferases, XylT is enzymatically active in the absence of added metal ions. This feature is not due to any metal ion directly associated with the enzyme. The precise acceptor substrate specificity of XylT was assessed with several physiologically relevant compounds and the xylosylated reaction products were subsequently tested as substrates of other Golgi-resident glycosyltransferases. These experiments revealed that the substrate specificity of XylT permits the enzyme to act at multiple stages of the plant N-glycosylation pathway.

The Drosophila melanogaster homologue of the human histo-blood group Pk gene encodes a glycolipid-modifying alpha1,4-N-acetylgalactosaminyltransferase.

Insects express arthro-series glycosphingolipids, which contain an alpha1,4-linked GalNAc residue. To determine the genetic basis for this linkage, we cloned a cDNA (CG17223) from Drosophila melanogaster encoding a protein with homology to mammalian alpha1,4-glycosyltransferases and expressed it in the yeast Pichia pastoris. Culture supernatants from the transformed yeast were found to display a novel UDP-GalNAc:GalNAcbeta1,4GlcNAcbeta1-R alpha-N-acetylgalactosaminyltransferase activity when using either a glycolipid, p-nitrophenylglycoside or an N-glycan carrying one or two terminal beta-N-acetylgalactosamine residues. NMR and MS in combination with glycosidase digestion and methylation analysis indicate that the cloned cDNA encodes an alpha1,4-N-acetylgalactosaminyltransferase. We hypothesize that this enzyme and its orthologues in other insects are required for the biosynthesis of the N5a and subsequent members of the arthro-series of glycolipids as well as of N-glycan receptors for Bacillus thuringiensis crystal toxin Cry1Ac.

Tracking interactions that stabilize the dimer structure of starch phosphorylase from Corynebacterium callunae. Roles of Arg234 and Arg242 revealed by sequence analysis and site-directed mutagenesis.

Glycogen phosphorylases (GPs) constitute a family of widely spread catabolic alpha1,4-glucosyltransferases that are active as dimers of two identical, pyridoxal 5'-phosphate-containing subunits. In GP from Corynebacterium callunae, physiological concentrations of phosphate are required to inhibit dissociation of protomers and cause a 100-fold increase in kinetic stability of the functional quarternary structure. To examine interactions involved in this large stabilization, we have cloned and sequenced the coding gene and have expressed fully active C. callunae GP in Escherichia coli. By comparing multiple sequence alignment to structure-function assignments for regulated and nonregulated GPs that are stable in the absence of phosphate, we have scrutinized the primary structure of C. callunae enzyme for sequence changes possibly related to phosphate-dependent dimer stability. Location of Arg234, Arg236, and Arg242 within the predicted subunit-to-subunit contact region made these residues primary candidates for site-directed mutagenesis. Individual Arg-->Ala mutants were purified and characterized using time-dependent denaturation assays in urea and at 45 degrees C. R234A and R242A are enzymatically active dimers and in the absence of added phosphate, they display a sixfold and fourfold greater kinetic stability of quarternary interactions than the wild-type, respectively. The stabilization by 10 mm of phosphate was, however, up to 20-fold greater in the wild-type than in the two mutants. The replacement of Arg236 by Ala was functionally silent under all conditions tested. Arg234 and Arg242 thus partially destabilize the C. callunae GP dimer structure, and phosphate binding causes a change of their tertiary or quartenary contacts, likely by an allosteric mechanism, which contributes to a reduced protomer dissociation rate.

Functional expression of a cDNA encoding pea (Pisum sativum L.) raffinose synthase, partial purification of the enzyme from maturing seeds, and steady-state kinetic analysis of raffinose synthesis.

Raffinose (O-alpha- D-galactopyranosyl-(1-->6)- O-alpha- D-glucopyranosyl-(1<-->2)- O-beta- D-fructofuranoside) is a widespread oligosaccharide in plant seeds and other tissues. Raffinose synthase (EC 2.4.1.82) is the key enzyme that channels sucrose into the raffinose oligosaccharide pathway. We here report on the isolation of a cDNA encoding for raffinose synthase from maturing pea ( Pisum sativum L.) seeds. The coding region of the cDNA was expressed in Spodoptera frugiperda Sf21 insect cells. The recombinant enzyme, a protein of glycoside hydrolase family 36, displayed similar kinetic properties to raffinose synthase partially purified from maturing seeds by anion-exchange and size-exclusion chromatography. Apart from the natural galactosyl donor galactinol ( O-alpha- D-galactopyranosyl-(1-->1)- L- myo-inositol), p-nitrophenyl alpha- D-galactopyranoside, an artificial substrate, was utilized as a galactosyl donor. An equilibrium constant of 4.1 was determined for the galactosyl transfer reaction from galactinol to sucrose. Steady-state kinetic analysis suggested that raffinose synthase is a transglycosidase operating by a ping-pong reaction mechanism and may also act as a glycoside hydrolase. The enzyme was strongly inhibited by 1-deoxygalactonojirimycin, a potent inhibitor for alpha-galactosidases (EC 3.2.1.22). The physiological implications of these observations are discussed.

Two closely related forms of UDP-GlcNAc: alpha6-D-mannoside beta1,2-N-acetylglucosaminyltransferase II occur in the clawed frog Xenopus laevis.

UDP-GlcNAc:alpha6-D-mannoside beta1,2-N-acetylglucosaminyltransferase II (GnT II; EC 2.4.1.143) is a medial-Golgi resident enzyme that catalyses an essential step in the biosynthetic pathway leading from high mannose to complex N-linked oligosaccharides. Screening a cDNA library from Xenopus laevis ovary with a human GnT II DNA probe resulted in the isolation of two cDNA clones encoding two closely related GnT II isoenzymes, GnT II-A and GnT II-B. Analysis of the corresponding genomic DNAs revealed that the open reading frame of both X. laevis GnT II genes resides within a single exon. The GnT II-A gene was found to be transcriptionally active in all X. laevis tissues tested. In contrast, expression of the GnT II-B gene was detected only in a limited number of tissues. Both GnT II-A and GnT II-B exhibit a type II transmembrane protein topology with a putative N-terminal cytoplasmic tail of 9 amino acids followed by a transmembrane domain of 18 residues, and a C-terminal luminal domain of 405 residues. The two proteins differ at 28 amino acid positions within their luminal regions. Heterologous expression of soluble forms of the enzymes in insect cells showed that GnT II-A and GnT II-B are both catalytically active and exhibit similar specific activities. Both recombinant proteins are modified with N-linked oligosaccharides. N-terminal deletion studies demonstrated that the first 49 amino acid residues are not essential for proper folding and enzymatic activity of X. laevis GnT II.