ABSTRACT
The effects of growth factors extracted from a newly established fetal lung fibroblast cell line (PMR-GF) on the melanocytes cultured from the perilesional and depigmented skins of vitiligo subjects and from normal healthy donors have been investigated. Melanocytes from normal subjects grown in the presence of 10 ng/ml of 12-0-tetradecanoyl phorbol 13-acetate and 10–11 Μ cholera toxin grew exponentially immediately after seeding the epidermal cell suspensions. Exogenous addition of PMR-GF to these cells enhanced their growth rates. The perilesional skin melanocytes of vitiligo subjects in most cases did not manifest any growth when cultured in the presence of 12-0-tetradecanoyl phorbol 13-acetate and cholera toxin. PMR-GF induced a brief burst of growth in these cells after a lag of 15 days. Vitiligo lesions gave rise to a few unpigmented dendritic cells that did not manifest any growth in the presence or absence of PMR-GF. Morphologically the perilesional skin melanocytes of most vitiligo subjects, when cultured in 12-0-tetradecanoyl phorbol 13-acetate and cholera toxin, appeared to be larger and hyper-melanotic as compared to those of normal individuals. In the presence of PMR-GF these melanocytes appeared to be normal in size and less hypermelanotic. Our results indicate that the melanocytes from vitiligo subjects are defective and thus the basic defect in vitiligo could be with the melanocytes themselves.
ABSTRACT
Phosphofructokinase (EC 2.7.1.11) from rabbit liver was purified to homogeneity. Preincubation of enzyme results in nonlinearity of enzyme activity with enzyme concentration. Therefore K0·5 of enzyme for fructose 6 phosphate in the absence or presence of fructose 2,6 bisphosphate or polyethylene glycol or in the presence of both was determined at physiological concentrations of its various effectors by taking the initial rate obtained by adding the enzyme last. They decrease the K0·5 value from 4·1 mM to about 0·2mM. The K0·5 of enzyme for fructose 2,6 bisphosphate was also determined under the above conditions. It is about 4·3 μΜ. Transient kinetics of phosphofructokinase at varying concentrations of enzyme in the presence of fructose 2,6 bisphosphate or polyethylene glycol or in the presence of both were studied. It was found that although they decrease t1/ 2 i.e. the time to reach half the maximal steady rate by about 5–8 fold, it was about constant at varying concentrations of the enzyme. These results indicate that fructose 2,6 bisphosphate and polyethylene glycol decrease K0·5 of the enzyme for fructose 6 phosphate not by associating the enzyme to higher aggregates, but by a different mechanism.