A prevalent mutation for galactosemia among black Americans

OBJECTIVE

To define the mutation causing galactosemia in patients of black American origin who have no galactose-1-phosphate uridyltransferase (GALT) activity in erythrocytes but good clinical outcome.

METHODS

We discovered a mutation caused by a C-->T transition at base-pair 1158 of the GALT gene that results in a serine-to-leucine substitution at codon 135 (S135L). We developed a method with which to screen populations for its prevalence. We compared galactose-1-phosphate uridyltransferase among erythrocytes, leukocytes, and transformed lymphoblasts, as well as total body oxidation of D-(13C)-galactose to 13CO2 among three genotypes for GALT (S135L/S135L, Q188R/Q188R, and Normal/Normal).

RESULTS

We found a 48% prevalence of the S135L mutation among 17 black American patients with classic galactosemia and a 1% prevalence in a population of 50 black Americans without galactosemia. The S135L mutation was not found in 84 white patients with G/G galactosemia nor in 87 white control subjects without galactosemia. We found normal whole body oxidation of D-(13C)-galactose by the patient homozygous for S135L and various degrees of enzyme impairment among different tissues.

CONCLUSIONS

The S135L mutation in the GALT gene is a prevalent cause of galactosemia among black patients. Because GALT activity varies in different tissues of patients homozygous for S135L, they may have a better clinical outcome than patients who are homozygous for Q188R when both are treated from infancy.

Inositol transport in Saccharomyces cerevisiae is regulated by transcriptional and degradative endocytic mechanisms during the growth cycle that are distinct from inositol-induced regulation

Regulation of inositol uptake activity in Saccharomyces cerevisiae during the growth cycle was examined. Activity increased as the cell population transited from lag phase to exponential growth, and continued to increase until late exponential phase. The increase in activity was due to increased transcription of the ITR1 gene and synthesis of the Itr1 permease. When the culture reached stationary phase, uptake activity decreased and dropped to a minimum within 4 h. The decrease was due to repression of ITR1 transcription, independent of the negative regulator Opi1p, and degradation of the existing permease. Degradation depended on delivery of the permease to the vacuole through the END3/END4 endocytic pathway. During exponential growth in inositol-containing medium the permease is also rapidly degraded, whereas in inositol-free medium the permease is highly stable. Rapid degradation of the permease at stationary phase occurred in inositol-free medium, indicating that there are two distinct mechanisms that trigger endocytosis and degradation in response to different physiological stimuli. In addition, the level of the enzyme required for inositol biosynthesis, inositol-1-phosphate synthase, encoded by INO1, is not reduced in stationary-phase cells, and this contrast in the regulation of inositol supply is discussed.

Pseudologia fantastica and gender identity disturbance in a Chinese male

A Chinese patient with pathological lying (pseudologia fantastica) and gender identity disturbance is described. The stories "save face" and lack a truly self-aggrandising quality. The importance of keeping "face" and maintaining modest behaviour in the Chinese culture is central to the psychopathology.

Characterization of P-S bond hydrolysis in organophosphorothioate pesticides by organophosphorus hydrolase

The extensive use of organophosphorothioate insecticides in agriculture has resulted in the risk of environmental contamination with a variety of broadly based neurotoxins that inhibit the acetylcholinesterases of many different animal species. Organophosphorus hydrolase (OPH, EC 3.1.8.1) is a broad-spectrum phosphotriesterase that is capable of detoxifying a variety of organophosphorus neurotoxins by hydrolyzing various phosphorus-ester bonds (P-O, P-F, P-CN, and P-S) between the phosphorus center and an electrophilic leaving group. OPH is capable of hydrolyzing the P-X bond of various organophosphorus compounds at quite different catalytic rates: P-O bonds (kcat = 67-5000 s-1), P-F bonds (kcat = 0.01-500 s-1), and P-S bonds (kcat = 0.0067 to 167 s-1). P-S bond cleavage was readily demonstrated and characterized in these studies by quantifying the released free thiol groups using 5,5'-dithio-bis-2-nitrobenzoic acid or by monitoring an upfield shift of approximately 31 ppm by 31P NMR. A decrease in the toxicity of hydrolyzed products was demonstrated by directly quantifying the loss of inhibition of acetylcholinesterase activity. Phosphorothiolate esters, such as demeton-S, provided noncompetitive inhibition for paraoxon (a P-O triester) hydrolysis, suggesting that the binding of these two different classes of substrates was not identical.

Regulation of inositol transport in Saccharomyces cerevisiae involves inositol-induced changes in permease stability and endocytic degradation in the vacuole

Uptake of inositol by Saccharomyces cerevisiae is mediated by a specific inositol permease encoded by the ITR1 gene. Removal of inositol from the growth medium results in an increase in ITR1 mRNA abundance. The increase in ITR1 mRNA is accompanied by an increase in de novo synthesis of the Itr1 permease leading to an increased capacity for uptake. When inositol is added to the growth medium inactivation of uptake activity occurs, and both transcription of ITR1 and uptake activity are repressed to a basal level of function. The transcriptional regulation of ITR1 depends on the INO2, INO4, and OPI1 genes. In addition, repression is also achieved by regulation of ITR1 expression at the post-translational level. In this study, we show that there is a change in the stability of the Itr1 permease after the addition of inositol to the growth medium. Immunoblot analysis using a monoclonal antibody against an epitope attached to the Itr1 permease showed that the addition of inositol causes a dramatic increase in the rate of degradation of the permease. After the repressed (basal) level is achieved, turnover continues to be rapid. The increased rate of degradation was also observed in strains with mutations that block conjugation to ubiquitin. Degradation was not observed in strains defective in the END3/END4 endocytic pathway or in the production of vacuolar proteases (PEP4). Thus, inactivation of the Itr1 permease is accompanied by endocytic internalization followed by degradation in the vacuole. Inactivation may be a separate process that precedes and signals endocytic degradation. Since the end3/end4 mutations did not affect uptake activity under derepressed conditions, endocytosis is not required for normal inositol uptake.

Bimetallic binding motifs in organophosphorus hydrolase are important for catalysis and structural organization

Organophosphorus hydrolase is a broad spectrum phosphoric acid hydrolase (EC 3.1.8.1) which appears to contain a binuclear metal center with two metals interactively involved in catalysis and/or structural functions. Site-directed mutagenesis has been employed to evaluate the participation of the various histidine and cysteine residues in metal coordination. The kinetic characteristics and metal binding stoichiometries of the purified site-directed substitutions of each of the histidine and cysteine residues in the catalytic domain of the protein to asparagine and serine residues, respectively, were determined. These data support the hypothesis that the histidines at positions 55, 57, and 201 are coordinated to a metal ion (M1) at the active center of the enzyme and that His254 and His257 are involved in the formation of a second structural metal center (M2). These and other unidentified amino acids may participate in a co-catalytic center. Although previous solution chemical studies concluded that cysteines are not involved in metal coordination, serine substitutions for Cys59 and Cys227 do affect metal content and catalytic activity. In contrast, substitution of asparagine for His230 does not affect the metal stoichiometry, but does reduce the kcat by 10(-4), indicating that it may be directly involved in the reaction chemistry. The H201N substitution eliminates activity but maintains one molar equivalent of metal and may function as a bridging ligand.

Dual control of inositol transport in Saccharomyces cerevisiae by irreversible inactivation of permease and regulation of permease synthesis by INO2, INO4, and OPI1

Uptake of inositol by Saccharomyces cerevisiae is regulated through transcriptional control of the gene that encodes the major inositol permease, ITR1 (Nikawa, J., Tsukagoshi, Y., and Yamashita, S. (1991) J. Biol. Chem. 266, 11184-11191). ITR1 mRNA abundance decreases when cells are transferred from medium without inositol to medium with inositol. Here we demonstrate that the mechanism of transcriptional regulation of ITR1 is through the action of the INO2, INO4 and OPI1 genes. INO2 and INO4 are required for derepressed levels of ITR1 mRNA, and OPI1 is necessary for repression of transcript levels in response to inositol. The INO2, INO4, and OPI1 genes thus coordinate uptake of inositol to endogenous inositol biosynthesis and to phospholipid biosynthesis. Repression of transcription of ITR1 also requires ongoing synthesis of phosphatidylcholine, defining an additional link between synthesis of phospholipids and regulation of inositol uptake. Analysis showed that the INO1 gene, encoding a key enzyme in the inositol biosynthetic pathway, responded to decreases in permease activity with a graduated increase in the level of INO1 mRNA. We also found that, in addition to the transcriptional regulation, inositol permease activity is regulated by irreversible inactivation. Inactivation of the ITR1 permease occurs in response to the presence of inositol and involves a change in the functional half-life of the protein.

Site of bone density measurement may affect therapy decision

The purpose of this study was to determine whether bone mineral density (BMD) measurements at the lumbar spine and femoral neck provided comparable information to women planning to use that knowledge to help them make a decision about hormone replacement therapy. Eighty-eight healthy Caucasian women, aged 44-59 and within 0 to 5 years of menopause, participated in the study. BMD measurements were performed at the lumbar spine (L1-L4) and the femoral neck by dual energy X-ray absorptiometry (DXA). Criteria suggested by the National Osteoporosis Foundation were used to categorize women as "at risk" for osteoporosis, bone density more than one standard deviation (SD) below the young adult mean, or as "low risk", bone density at or above this level. The results indicated that 46 women would be classified into the low risk category on the basis of spinal BMD alone. However, 28 of these 46 women would fall into the at risk category when the femoral neck BMD was measured. Sixty-one percent of women informed they were at low risk on the basis of spinal BMD would be considered at risk based on femoral neck BMD. When femoral neck BMD was used as the primary risk indicator, 14% of the women classified as low risk would be at risk if spinal BMD were added. These results suggest that both lumbar spine and proximal femur measurements should be made when women are using bone density measurements as an aid in deciding whether or not to use hormone therapy in their postmenopausal years.

31P NMR spectra of ethidium, quinacrine, and daunomycin complexes with poly(adenylic acid).poly(uridylic acid) RNA duplex and calf thymus DNA

31P NMR provides a convenient monitor of the phosphate ester backbone conformational changes upon binding of the intercalating drugs ethidium, quinacrine, and daunomycin to sonicated poly(A).poly(U) and calf thymus DNA. 31P chemical shifts can also be used to assess differences in the duplex unwinding angles in the presence of the drug. Thus a new 31P signal, 1.8-2.2 ppm downfield from the double-stranded helix signals, is observed in the ethidium ion-poly(A).poly(U) complex. This signal arises from phosphates which are in perturbed environments due to intercalation of the drug. This is in keeping with the hypothesis that the P-O ester torsional angle in phosphates linking the intercalated base pairs is more trans-like. Similar though smaller deshielding of the 31P signals is observed in sonicated poly(A).poly(U)-quinacrine complexes as well as in the daunomycin complexes. The effect of added ethidium ion, quinacrine, and daunomycin on the 31P spectra of sonicated calf thymus DNA is consistent with Wilson and Jones' (1982) earlier study. In these drug-DNA complexes the drug produces a gradual downfield shift in the DNA 31P signal without the appearance of a separate downfield peak. These differences are attributed to differences in the rate of chemical exchange of the drug between free and bound duplex states. The previous correlation of 31P chemical shift with drug duplex unwinding angle (Wilson & Jones, 1982) is confirmed for both the RNA and DNA duplexes.

Subacute myelopathy: an unusual paraneoplastic complication of Hodgkin's disease

We report a case of Hodgkin disease presenting with a subacute myelopathy without evidence of metastatic involvement of the spinal cord. The systemic disease responded to conventional chemotherapy, but the myelopathy only improved after intrathecal dexamethasone was added to the treatment program, beta-2-microglobulin levels in the cerebrospinal fluid were elevated at presentation. Following the use of intrathecal corticosteroids there was a decrease of CSF beta-2-microglobulin levels. The possible significance of these findings is discussed.

Spatial distribution and size of acetylcholine receptor clusters determined by motor nerves in developing chick muscles

The size and distribution of acetylcholine receptor clusters (AChR-C) on normal and aneural developing muscle fibres of the chick wing were studied by labelling AChR with fluorescent conjugates of alpha-bungarotoxin (alpha-BGT). AChR-C of a size typical of initial synaptic contacts (5 micron long) were present at 7 days incubation, shortly after the appearance of nerves, and were grouped in bands corresponding to muscle nerve branches. A regular distribution of large (approximately equal to 5 micron) AChR-C separated by 100-200 micron had developed by 10-14 days in the slow-tonic anterior latissimus dorsi and ulnimetacarpalis dorsalis muscles. The role of motor innervation in the formation of AChR-C was assessed by removing the brachial neural tube at 2 days incubation in order to prevent nerves entering the wing. Neural-tube removal prevented the appearance of the large AChR-C normally associated with the early synaptic contacts. Small AChR-C (less than 2 micron long) appeared in aneural muscles, but these were not grouped into bands characteristic of the large AChR-C in normal muscles. The results suggest that the formation of junctional AChR-C is dependent on nerves.

31P and two-dimensional 31P/1H correlated NMR spectra of Duplex d(Ap[17O]Gp[18O]Cp[16O]T) and assignment of 31P signals in d(ApGpCpT)2-actinomycin D complex

A solid-phase phosphoramidite method was used for the synthesis of unlabeled and phosphoryl-labeled d(Ap-[17O]Gp[18O]Cp[16O]T). The ability to label the phosphoryl oxygens of d(ApGpCpT) and thus assign the 31P signals, combined with a two-dimensional 31P/1H chemical shift correlated NMR spectral technique, provided a novel means for the ready assignment of the H5' and H3' protons coupled to the phosphates. Phosphoryl labeling has also allowed us to assign the 31P NMR signals in the actinomycin D-d(Ap-[17O]Gp[18O]Cp[16O]T)2 duplex complex and confirm that the drug intercalates between the GpC stacked base pairs.

A two-dimensional NMR method for assignment of deoxyribose proton NMR signals in d(ApGpCpT)

The ability to label the phosphoryl oxygens of d( ApGpCpT ) and thus assign the 31P signals, combined with a 2-D 31P/1H chemical shift correlated NMR spectral technique, provides a novel means for the ready assignment of the H5' and H3' protons coupled to the phosphates.

Phosphorus-31 nuclear magnetic resonance of double- and triple-helical nucleic acids. Phosphorus-31 chemical shifts as a probe of phosphorus-oxygen ester bond torsional angles

The temperature dependence to the 31P NMR spectra of poly[d(GC)] . poly [d(GC)],d(GC)4, phenylalanine tRNA (yeast) and mixtures of poly(A) + oligo(U) is presented. The 31P NMR spectra of mixtures of complementary RNA and of the poly d(GC) self-complementary DNA provide torsional information on the phosphate ester conformation in the double, triple, and "Z" helix. The increasing downfield shift with temperature of the single-strand nucleic acids provides a measure of the change in the phosphate ester conformation in the single helix to coil conversion. A separate upfield peak (20-60% of the total phosphates) is observed at lower temperatures in the oligo(U) . poly(A) mixtures which is assigned to the double helix/triple helix. Proton NMR and UV spectra confirm the presence of the multistrand forms. The 31P chemical shift for the double helix/triple helix is 0.2-0.5 ppm upfield from the chemical shift for the single helix which in turn is 1.0 ppm upfield from the chemical shift for the random coil conformation.