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Biomedical subjects

A Ramaiah

Publications and source records attributed to A Ramaiah.

At least 19 recordsLinked to original sources
PubMed1989

Growth defects of melanocytes in culture from vitiligo subjects are spontaneously corrected in vivo in repigmenting subjects and can be partially corrected by the addition of fibroblast-derived growth factors in vitro.

Melanocytes cultured from uninvolved skin of untreated vitiligo subjects have decreased initial seeding capacities, manifest a lag period for the onset of the growth phase, and cannot be passaged. In contrast, melanocytes obtained from uninvolved and perilesional skin of vitiligo subjects actively repigmenting under 8-methoxy psoralen plus sunlight (PUVA) therapy have higher initial seeding capacities, grow faster without a lag period, and can be passaged to more than 12 passages. Extracts of a fetal lung fibroblast cell line (PMR-GF) that promote the growth rates and passage capacities of melanocytes from normal adult donors have been found also to promote the growth rates and passage capacities of melanocytes from the uninvolved skin of vitiligo subjects. Extracts of a fetal lung fibroblast cell line (PMR-GF), however, did not have any further stimulatory effect on the growth of melanocytes obtained from repigmenting vitiligo subjects. Melanocytes cultured from normal and untreated vitiligo subjects grew individually dispersed in the absence of PMR-GF, but tended to grow in clusters in its presence. Melanocytes from the repigmenting vitiligo subjects, however, tended to grow in clusters even in the absence of PMR-GF. These results indicate that the defective in vitro growth characteristics of melanocytes from vitiligo subjects may be related to the pathogenesis of this disease. It is possible that growth factors may be involved in the process of repigmentation in vitiligo subjects.

Adolescent↗
PubMed1989

Etiology of vitiligo. A new hypothesis.

Serum from actively repigmenting human vitiligo subjects had maximum mitogenic effect on the growth of melanocytes in culture, followed by the serum from normal donors, and from untreated vitiligo subjects in that order. Based on these findings, a new hypothesis is suggested for the etiology of vitiligo.

Adult↗
PubMed1988

pH-dependent interconversion of two forms of tyrosinase in human skin.

1. We have shown that the characteristic lag in cresolase activity of human skin tyrosinase at inhibitory concentration of tyrosine was absent at all pH values studied, i.e. pH 5.2, 5.7, 6.2 and 6.8, if the enzyme solubilized at low pH was used as the source of enzyme, but the same enzyme when dialysed against buffers of various pH values showed linear activity only at pH 5.2 and was not inhibited by excess tyrosine, whereas at higher pH values it exhibited a lag and inhibition by excess tyrosine. 2. However, the enzyme solubilized in buffer/detergent, pH 6.8, when dialysed against buffer of the same pH showed linear activity at pH 5.2 and non-linear activity at pH 6.8. 3. The water/detergent-solubilized enzyme from human skin melanosomes showed linear activity even at inhibitory concentrations of tyrosine at pH 5.2 and 6.8 up to 2 h, but acceleration of rate was observed after 2 h for the enzyme measured at pH 6.8. 4. After dialysis of the water/detergent-solubilized enzyme against double-glass-distilled water, it still exhibits linear activity at inhibitory concentration of tyrosines at pH 6.8 for the first 2 h, but the same enzyme when dialysed against 0.02 M-sodium phosphate buffer, pH 6.8, exhibits negligible activity up to 1/2 h, in contrast with considerable activity before dialysis during the same interval of time, but without any loss of activity at later intervals of incubation time. 5. On the basis of these results, it is concluded that the enzyme exists in at least two interconvertible forms, one without lag and inhibition by excess tyrosine and the other with lag and inhibition by excess tyrosine. These two forms are interconvertible only by gradual change in pH over a period of hours.

Catechol Oxidase↗
PubMed1987

pH-dependent interconvertible allosteric forms of murine melanoma tyrosinase. Physiological implications.

Murine melanoma melanosomal tyrosinase, solubilised at pH 6.8 and 1% Igepal, exhibits a lag in cresolase activity which increases with increasing concentration of tyrosine. The enzyme, solubilised at pH 5.0 and assayed at pH 5.0, does not exhibit lag even at inhibitory concentrations of tyrosine while the same enzyme when assayed at pH 6.8 exhibits characteristic lag. When the enzyme was solubilised from a melanosomal fraction with detergent/water without any buffer, significant linear activity for 2 h was seen at an inhibitory concentration of tyrosine, indicating for the first time the presence of a form of tyrosinase without lag and inhibition by excess tyrosine. Exposure of the enzyme solubilised in buffer/detergent at pH 6.8 to rapid decrease in pH to 5.0 or 4.7 makes the enzyme remain irreversibly in the form without characteristic lag, even at an inhibitory concentration of tyrosine and at pH 6.8. These results may be interpreted as follows. The enzyme at pH 6.8 exists in the E form with an allosteric site for tyrosine. Decrease of the pH of the enzyme solution from 6.8 to 5.0 or 4.7 by dialysis results in the reversible protonation of the enzyme, which no longer binds tyrosine at its allosteric site and consequently inhibition by excess tyrosine and lag were not observed at acidic pH. However, if the enzyme was rapidly brought to pH 5.0 from 6.8 it remains irreversibly in the protonated form even at pH 6.8. Ascorbic acid acts as an effective reductant for the hydroxylation of tyrosine by tyrosinase, while 3,4-dihydroxyphenylalanine is both an effective reductant and counteracts the inhibition by tyrosine at pH 6.8.

Allosteric Regulation↗
PubMed1987

In vitro growth characteristics of melanocytes obtained from adult normal and vitiligo subjects.

The in vitro growth characteristics of melanocytes obtained from uninvolved and perilesional skin of vitiligo vulgaris subjects have been investigated in comparison to those from healthy adult donors. Normal human melanocytes have been found to grow exponentially in the presence of 10(-11) M cholera toxin and 10 ng/ml of 12-O-tetradecanoylphorbol-13-acetate in routine tissue culture media. They could be trypsinized up to 3-4 passages. Melanocytes of the uninvolved skin of vitiligo subjects manifested a lag of 8-11 days for the onset of growth and they could not be passaged. Melanocytes obtained from both hypo- and hyper-pigmented perilesional skin failed to grow under these conditions. Only in a few cases where the perilesional skin was normally pigmented did the melanocytes manifest some growth after a lag of 15 days. The initial seeding capacity of the melanocytes from uninvolved and perilesional skin of vitiligo patients were, respectively, 50% and 25% of the normal individuals. Vitiligo lesions themselves gave rise to unidentified dendritic cells that survived for 10-15 days without manifesting any growth. Our results suggest that melanocytes of individuals with vitiligo are defective. This fact has to be taken into account in any theory on the etiology of vitiligo.

Adolescent↗
PubMed1971

Properties of phosphofructokinase from the mucosa of rat jejunum and their relation to the lack of Pasteur effect.

1. The properties of phosphofructokinase after its slight purification from the mucosa of rat jejunum were studied. 2. The enzyme is inhibited by almost 100% by an excess of ATP (1.6mm), with 0.2mm-fructose 6-phosphate. AMP, ADP, P(i) and NH(4) (+) at 0.2, 0.76, 1.0 and 2mm respectively do not individually prevent the inhibition of phosphofructokinase activity by 1.6mm-ATP with 0.2mm-fructose 6-phosphate to any great extent, but all of them together completely prevent the inhibition of phosphofructokinase by ATP. 3. One of the effects of high concentrations of ATP on the enzyme was to increase enormously the apparent K(m) value for the other substrate fructose 6-phosphate, and this increase is largely counteracted by the presence of AMP, ADP, P(i) and NH(4) (+). At low concentrations of ATP the above effectors individually decrease the concentration of fructose 6-phosphate required for half-maximum velocity and when present together they decrease it further, in a more than additive way. 4. When fructose 6-phosphate is present at a saturating concentration (5mm), 0.3mm-NH(4) (+) increases the maximum velocity of the reaction 3.3-fold; with 0.5mm-fructose 6-phosphate, 4.5mm-NH(4) (+) is required for maximum effect. The other effectors do not change the maximum reaction velocity. 5. The results presented here suggest that NH(4) (+), AMP, ADP and P(i) synergistically decrease the inhibition of phosphofructokinase activity at high concentrations of ATP by decreasing the concentration of fructose 6-phosphate required for half-maximum velocity. Such synergism among the effectors and an observed, low ;energy charge' [(ATP+(1/2)ADP)/(AMP+ADP+ATP)] in conjunction with the possibility of a relatively high NH(4) (+) and fructose 6-phosphate concentration in this tissue, may keep the mucosal phosphofructokinase active and uninhibited by ATP under aerobic conditions, thus explaining the high rate of aerobic glycolysis and the lack of Pasteur effect in this tissue.

Adenosine Diphosphate↗