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Biomedical subjects

M D Jeyasingham

Publications and source records attributed to M D Jeyasingham.

8 recordsLinked to original sources
PubMed1989

Interaction between pyridine nucleotide coenzymes and heme proteins as a possible source of error in assay of activities of coenzyme-linked enzyme.

The ultraviolet absorbance spectra of pyridine nucleotide coenzymes change in the presence of heme-containing proteins. The positions of each of the two main absorbance peaks of NADH are shifted progressively towards shorter wavelengths in the presence of increasing concentrations of hemoglobin, and the third peak, at 220 nm, disappears altogether. Similar changes are seen in the spectra of NAD+ and NADPH, and similar effects on these spectra are produced by myoglobin and cytochrome c, but not by comparable concentrations of albumin. The spectral shifts are generally accompanied by a decreased peak height. This finding may help explain problems reported by previous workers in the measurement of the activity of enzymes such as transketolase or lactate dehydrogenase in erythrocyte hemolysates. Errors may be considerable if allowance is not made for this effect, especially if the concentration of heme protein in the spectrophotometer cuvette much exceeds 1 g/L. The interaction appears to indicate some form of bonding, occurring generally between pyridine nucleotide coenzymes and the heme group in proteins. We relate the findings to measurement of activities of pyridine nucleotide-linked enzymes in erythrocyte lysates and in plasma containing myoglobin after muscle breakdown.

Coenzymes↗
PubMed1988

Rat brain apotransketolase: activation and inactivation.

Kinetic analysis of the combination of rat brain apotransketolase with thiamine diphosphate suggested that the enzyme exists in more than one form. One part of the apoenzyme reacted rapidly with thiamine diphosphate to reconstitute the holoenzyme, but another part appeared to combine only relatively slowly. In addition, an apparently irreversible further change took place, the apoenzyme being converted progressively to a form which apparently could not be activated by thiamine diphosphate. The relative proportions of the three forms i.e., that reacting rapidly, slowly, or not at all with thiamine diphosphate, were a function of the duration and conditions of storage, with the proportion of the apoenzyme form which reacted rapidly with thiamine diphosphate decreasing progressively. The findings reported here provide a possible explanation for problems various workers have encountered in attempting to evaluate Michaelis constants for the reaction of thiamine diphosphate with apotransketolase.

Animals↗
PubMed1987

Decrease in oligodendrocyte carbonic anhydrase activity preceding myelin degeneration in cuprizone induced demyelination.

Both immunohistochemical and biochemical evidence is presented to show for the first time that carbonic anhydrase II (CA II) activity falls in the brain of mice in cuprizone (bis(cyclohexanone)oxalyldihydrazone) induced demyelination well before demyelination develops. This fall began during the first week, whereas the first signs of myelin degeneration induced by cuprizone did not appear until 3 weeks and demyelination in the superior cerebellar peduncle in the mouse took 6-8 weeks to develop. The findings suggest that oligodendrocyte CA II activity is essential either for the survival of oligodendrocytes or for the maintenance of central myelin.

Animals↗
PubMed1987

The activation of red blood cell transketolase in groups of patients especially at risk from thiamin deficiency.

Erythrocyte transketolase activation by thiamin diphosphate has been studied in elderly patients with moderate or severe chronic dementia, acute alcoholic admissions and chronic alcoholics with evidence of brain damage, mostly of the Wernicke-Korsakoff type. Significantly more patients in each group than controls showed abnormal activation of transketolase, not only by 0.3 mM thiamin diphosphate (TDP) but also in further activation by increase to 3 mM. This indicated the presence in a proportion of the alcoholic and the demented patients of an abnormal enzyme variant, similar to that previously found in vitro. The modified transketolase activation test may warn not only of marginal thiamin deficiency but also independently, of susceptibility to brain damage in patients at risk.

Adult↗
PubMed1987

Nutrition and alcoholic encephalopathies.

An assessment has been made of metabolic factors possibly causing or contributing to the brain damage associated with chronic alcoholism, especially thiamin lack or disturbance of amino acid metabolism. Abnormalities in the thiamin-dependent enzyme, transketolase, provide evidence of a high incidence of thiamin deficiency as well as of disturbed thiamin metabolism in chronic alcoholics, which are likely to be caused by reduced vitamin intake as well as impaired absorption. A grossly disturbed pattern of amino acids in the blood of patients undergoing treatment for alcohol withdrawal syndromes is likely to be caused by loss of hepatic function and may well aggravate brain damage caused by B group vitamin deficiency. A hypothesis is proposed of how chronic thiamin lack can lead to brain damage.

Alcoholism↗
PubMed1987

Changes in the activation of red blood cell transketolase of alcoholic patients during treatment.

Erythrocyte transketolase activation by thiamin diphosphate has been studied in alcoholic patients on admission and after treatment, which included vitamin therapy. The high proportion of the patients who showed an abnormal activation of transketolase, not only by 0.3 mM thiamin diphosphate but also further activation by increasing the thiamin diphosphate to 3 mM, was reduced considerably after treatment. A few patients, however, still showed continuing abnormalities even after treatment. Further study of the enzyme activation in vitro confirmed the presence of an enzyme variant, abnormal both in the ease with which the thiamin diphosphate could be removed and in requiring a high concentration of thiamin diphosphate for activation. Since the modified transketolase activation test appears not only to monitor the effectiveness of thiamin therapy but also independently to warn of persisting enzyme abnormalities, it could prove to be of general use in alcohol detoxification units.

Adult↗
PubMed1986

Reduced stability of rat brain transketolase after conversion to the apo form.

The stability of rat brain transketolase, whether measured at 37 or 0 degree C, was reduced after conversion to the apo form by removal of thiamine diphosphate, as shown by a decline in the activity recovered when assayed in the presence of thiamine diphosphate. Both the shape of the breakdown curve and the failure to recover the full activity, even after incubation with thiamine diphosphate, showed that the breakdown of the apotransketolase was complex. The initial rate of breakdown of the apoenzyme was sharply pH dependent, being minimal at 37 degrees C at a pH value of 7.6, close to that likely to exist in vivo. The rate rose sharply with deviation of the pH in either direction. The stability of the enzyme on storage at 0 degree C showed a similar pattern of pH dependence, provided that allowance is made for temperature effects on dissociation constants. These findings provide further support for the hypothesis that differences in brain transketolase may play a part in the etiology of Wernicke-Korsakoff's syndrome.

Animals↗