Table 2.

Relative Abundance of Sphingomyelin Species in Lipid Rafts and PNS

		PNS		Detergent-free		Brij 98		Triton X-100
m/z	Assignment	Average (nmol/mg protein)	% Total Sphingomyelin	Average (nmol/mg protein)	% Total Sphingomyelin	Average (nmol/mg protein)	% Total Sphingomyelin	Average (nmol/mg protein)	% Total Sphingomyelin
707.5	N16:1	1.27	3.61	12.88	4.99	71.26	6.74	47.60	4.17
709.5	N16:0	17.87	50.82	209.07	81.04	703.74	66.54	840.36	73.58
735.5	N18:1	0.26	0.75	0.99	0.38	2.51	0.24	2.51	0.22
737.5	N18:0	0.69	1.95	3.50	1.36	7.16	0.68	10.76	0.94
765.5	N20:0	11.36	32.31	6.09	2.36	145.45	13.75	121.80	10.66
817.5	N24:2	0.96	2.73	3.69	1.43	22.38	2.12	18.02	1.58
819.5	N24:1	2.24	6.36	17.15	6.65	84.18	7.96	80.10	7.01
821.5	N24:0	0.51	1.46	4.63	1.79	20.87	1.97	21.04	1.84
	Total	35.17	100.00	257.99	100.00	1057.54	100.00	1142.18	100.00

The fractional abundance of each species was calculated by dividing the nmol/mg protein of that species by the total nmol/mg protein of Sphingomyelin present in that particular membrane preparation and multiplying by 100. Data represent the average of three experiments. The absolute abundance data are given in Supplemental Table I.