J. Biol. Chem., Vol. 262, Issue 34, 16391-16393, Dec, 1987
Polyamines stimulate lysosomal cystine transport
AJ Jonas, LJ Symons and RJ Speller
Department of Pediatrics, University of Texas Medical School, Houston 77030.
Lysosomal cystine transport is a carrier-dependent process that, in
isolated lysosomes, is stimulated by proton gradients, membrane potential,
and millimolar concentrations of divalent cations. The importance of these
regulatory factors in vivo is not well established. Polyamines were found
to stimulate cystine transport in Percoll gradient purified rat liver
lysosomes with spermidine greater than putrescine = cadaverine greater than
spermine in order of effectiveness. Maximal stimulation was achieved with
500 microM spermidine. The effects of optimal concentrations of polyamines
and divalent cations on cystine transport were not additive. Spermidine
stimulated cystine efflux from lysosomes of cultured human diploid
fibroblasts, but had no effect on lysosomes of cystinotic fibroblasts which
have defective cystine transport. Spermidine did not accumulate within
lysosomes in exchange for cystine, had no effect on lysosomal pH, had only
slight effects on the lysosomal membrane potential, and had little effect
on either methionine or tyrosine efflux. Polyamines are cellular
cytoplasmic components that, in physiologic concentrations, stimulate
lysosomal cystine transport.
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