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Biomedical subjects

L Tsai

Publications and source records attributed to L Tsai.

At least 91 records · Page 5Linked to original sources
PubMed1984

Distribution of two selenonucleosides among the selenium-containing tRNAs from Methanococcus vannielii.

Naturally occurring seleno-tRNAs from Methanococcus vannielii account for 13-20% of the total tRNA population. Two different selenium-modified nucleosides were detected in these seleno-tRNAs. Of the total selenium incorporated, about 60% is present in 5-methylaminomethyl-2-selenouridine, and the other 40% occurs in a second selenonucleoside with spectral characteristics typical of a derivative of 2-selenouridine. The 5-methylaminomethyl-2-selenouridine was found in the seleno-tRNA species present in the early fractions of a linear salt gradient elution profile from a reversed-phase chromatographic system 5 (RPC-5) column, whereas the second selenonucleoside occurred in the tRNA species eluted late in the profile.

Chromatography, High Pressure Liquid↗
PubMed1982

Analogues of 8-hydroxy-5-deazaflavin cofactor: relative activity as substrates for 8-hydroxy-5-deazaflavin-dependent NADP+ reductase from Methanococcus vannielii.

The 8-hydroxy-5-deazaflavin-dependent NADP+ reductase from Methanococcus vannielii was examined for its ability to catalyze the reduction of a number of 5-deazaflavin analogues of the natural cofactor. Comparison of the kinetic constants revealed certain substrate structure-reactivity relationships for the enzyme. The basic heterocyclic system of the natural cofactor 2,4-dioxopyrimido [4,5-b]quinoline was shown to be the minimum structural requirement since neither riboflavin nor 1,5-dideazariboflavin was reduced by the enzyme. The N-10 side chain of the natural cofactor was shown not to be essential since the enzyme could reduce 8-hydroxy-2,4-dioxopyrimido[4,5-b]quinoline. The study also indicated that there are some steric constraints at C-8 and C-7 with respect to interaction of the cofactor with the enzyme. Specifically, (a) the 8-methoxy derivative, in contrast to the 8-hydroxy compound, was not reduced and (b) the introduction of a substituent at C-7 resulted in a marked decrease in the rate of reduction. The importance of C-5 as the site for the electron entry was suggested by the finding that 5-methyl-deazariboflavin was not reduced. The latter inhibited the reduction of 5-deazariboflavin.

Euryarchaeota↗
PubMed1982

Social class distribution of fathers of children enrolled in the Iowa Autism Program.

The social class distribution of fathers with autistic children attending a locally well-known and state-supported modern autism program was examined and was compared to the social class distributions observed in a nonautistic, mentally retarded population, in children with other psychiatric disorders, and in the general population from which the present autistic sample was drawn. No significant differences were found among the groups. The findings supported the view that if studies are not biased by certain selection factors outside the autistic child's clinical picture and diagnosis, and if services become better known and readily available, then no differences in social class distribution between autistic and nonautistic groups occur. The results suggest that social class is not an important factor in the origin of autistic syndrome.

Autistic Disorder↗
PubMed1982

Unfavourable left-right asymmetries of the brain and autism: a question of methodology.

Thirty-six patients with infantile autism and various neurological disorders underwent computerized tomographic (CT) scanning of the brain. All CT scans were assessed blindly and independently by a diagnostic radiologist. Two techniques modified from two previous studies were used for measuring parieto-occipital asymmetry. The frequency of reversed asymmetry in autistic patients was the same as that in patients with various neurological disorders, and there was no significant association between reversed asymmetry and delayed language development. The study does not support the concept that unfavourable morphological asymmetries of the brain near the posterior language zone may contribute to the difficulties autistic children experience in acquiring language. Methodological difficulties and the design of new studies are discussed.

Adolescent↗
PubMed1981

Implication of sex differences in the familial transmission of infantile autism.

There are studies suggesting possible hereditary influence in autism. Data on 102 autistic children, 78 boys and 24 girls, showed that there was a significantly greater proportion of autistic girls than boys with IQs less than 50 and with evidence of brain damage. The autistic girls also had a greater proportion of relatives affected with autism or cognitive-language deficit than did the boys. The implication of sex differences in the possible mode of familial transmission of autism is discussed.

Adolescent↗
PubMed1981

The incidence of cognitive disabilities in the siblings of autistic children.

Individual components of cognitive disability were assessed in the siblings of 41 autistic probands and compared with similar measures from a control group of siblings of Down's syndrome individuals. The results showed a significant familial clustering of cognitive disabilities in the siblings of autistic probands. These cognitive impairments included disturbances in expressive and receptive language, specific learning disabilities, and varying degrees of mental subnormality.

Adolescent↗
PubMed1981

How can we avoid unnecessary CT scanning for psychiatric patients.

We studied 135 psychiatric patients who had CT scans of the brain in addition to psychiatric mental status examination (ME), neurological examination (NE), EEG and Canter's Background Interference Procedure for the Bender Gestalt Test (BIP). The results suggested that CT scans were unnecessary in about a quarter of these patients. Those who had normal ME, NE, EEG and BIP could safely be excluded. Those who had normal ME and NE but abnormal BIP or EEG could also be excluded if they were 40 years or younger with no history of head injury.

Adolescent↗
PubMed1980

Stereochemical studies of 8-hydroxy-5-deazaflavin-dependent NADP+ reductase from Methanococcus vannielii.

The purified 8-hydroxy-5-deazaflavin-dependent NADP+ reductase from Methanococcus vannielii catalyzes an oxidation-reduction reaction between a novel 8-hydroxy-5-deazaflavin cofactor and nicotinamide adenine dinucleotide phosphate. The reaction was shown to be a direct hydride transfer process. Using stereospecifically 3H-labeled substrates, the steric course of this process was established to be S-specific with respect to the nicotinamide nucleotide. The 8-hydroxy-5-deazaflavin-dependent NADP+ reductase from M. vannielii and the hydrogenase system in the cell-free extracts of Methanobacterium thermoautotrophicum recognize the same side, designated as A side, with respect to the prochiral center at C-5 of the dihydro-8-hydroxy-5-deazaflavin cofactor.

Euryarchaeota↗
PubMed1980

Purification and properties of 8-hydroxy-5-deazaflavin-dependent NADP+ reductase from Methanococcus vannielii.

The 8-hydroxy-5-deazaflavin-dependent NADP+ reductase component of the formate NADP+ oxidoreductase system of Methanococcus vannielii has been purified to homogeneity. The enzyme is specific for NADP+ and 8-hydroxy-5-deazaflavin. It catalyzes the reaction: 1,5-Dihydro-8-hydroxy-5-deazaflavin anion + NADP+ in equilibrium 8-hydroxy-5-deazaflavin + NADPH. The apparent molecular weight of the native enzyme is 85,000. A subunit molecular weight of 43,000 determined by sodium dodecyl sulfate gel electrophoresis indicates that the native enzyme is a dimer. The optimal temperature for catalytic activity is 17-20 degrees C and the pH maxima are 7.9 and 4.8 for the forward and reverse reactions, respectively. The kcat value of the forward reaction is 24 times greater than that of the reverse reaction, thus the production of NADPH at pH 7.0 is more favorable than its consumption. The reductase contains one or more sulfhydryl groups which are essential for catalytic activity.

Chemical Phenomena↗
PubMed1980

Relative efficacy of computed tomography and radionuclide scan in the diagnosis of organic brain syndrome.

Computerized tomography (CT) scan and radionuclide (Rn) scan findings on 77 psychiatric patients were compared to evaluate the relative efficacy of these two procedures in the diagnosis on intracranial disease. CT scan detected significant abnormalities in 23 patients (29.9%) while the Rn scan was positive in only five patients (6.5%). This is almost a fivefold difference in the detection rate of abnormalities between the CT and RN scan. Thirty-four of the 77 patients were diagnosed with organice brain syndrome (OBS) according to the criteria by Feighner et al. CT scan exclusively determined the contributing causes in 20 (58.8%) of these patients. In contrast, none of the Rn studies could exclusively contribute to a diagnosis of OBS. It is concluded that the routine use of both diagnostic procedures hardly seems justifiable in terms of patient benefit and increased cost.

Adolescent↗
PubMed1979

The Mini-Mental State Test and computerized tomography.

In order to evaluate the clinical usefulness of the Mini-Mental State (MMS) test, the authors had 63 patients complete the test after undergoing computerized tomographic (CT) scans of the brain. Patients with positive CT scans scored significantly lower than those with negative CT scans. Further analysis showed that cerebral atrophy was more closely related to cognitive impairment than focal cerebral lesions only. The authors conclude that the MMS can discriminate organicity in some instances but that further refinement and modification of its subtests are needed for maximum usefulness.

Aged↗
PubMed1970

Nicotinic acid metabolism. V. A cobamide coenzyme-dependent conversion of alpha-methyleneglutaric acid to dimethylmaleic acid.

A new B(12)-coenzyme-dependent isomerization, catalyzed by extracts of a nicotinate-fermenting clostridium, results in the conversion of alpha-methyleneglutaric acid to dimethylmaleic acid. These two acids are intermediates in the multistep anaerobic process wherein nicotinate is converted, ultimately, to one mole each of propionate, acetate, carbon dioxide, and ammonia. Dimethylmaleic acid reacts in its anhydride form with 2,4-dinitrophenylhydrazine to form N-2',4'-dinitrophenyl-anilino-3,4-dimethylmaleimide. The characteristic reddish color exhibited by the latter derivative in alkaline solution serves as a convenient quantitative assay for dimethylmaleic acid. Comparison of the 2,4-dinitrophenylhydrazine derivatives of the product of the enzymic reaction and of synthetic dimethylmaleic anhydride showed them to be identical in every respect.

Acetates↗