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245	1	0	_aDifferential effects of spermine on phosphatidylinositol 3-kinase and phosphatidylinositol phosphate 5-kinase
490	0		_vLife Science , 57(7), p.685-694, 1995
520	3		_aThe metabolism of phosphoinositides plays an important role in the signal transduction pathways. We report here that naturally occurring polyamines affect the activities of phosphatidylinositol (PI)3-kinase and PI 4-phosphate (PIP)5-kinase differently. While polyamines inhibited the PI 3-kinase activity, they stimulated the activity of PIP 5-kinase in the order of spermine > spermidine > putrescine. Spermine inhibited the PI 3-kinase activity in a concentration-dependent manner with an IC50 of 100 microM. On the other hand, spermine (5 mM)stimulated the activity of PIP 5-kinase 2-3 fold. Kinetic studies of spermine-mediated inhibition of PI 3-kinase revealed that it was noncompetitive with respect to ATP. The effect of Mg2+ and PIP2 concentration on kinase activity was sigmoidal, with spermine inhibiting PI 3-kinase activity at all PIP2 concentrations. While 1 mM calcium stimulated PI 3-kinase activity at submaximal concentrations of Mg2+ (1.25 mM), inhibition was observed at optimal concentration of Mg2+ (2 mM). We propose that spermine may modulate the cellular signal by virtue of its differential effects on phosphoinositide kinases.
700	1	2	_aSingh, S.S.
856	4	0	_uhttps://drive.google.com/file/d/1ItngNQPrVNi9ZqSJBJUjntVJa0mcOf0V/view?usp=drivesdk _zPara ver el documento ingresa a Google con tu cuenta: @cicy.edu.mx
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