Sphingomyelinase D activity of brown recluse spider (Loxosceles reclusa) venom as studied by 31P-NMR: effects on the time-course of sphingomyelin hydrolysis.

The time-course for the hydrolysis of the D linkage of chicken egg yolk sphingomyelin in a Triton X-100 mixed micelle and of lysophosphotidylcholine micelles, as catalyzed by brown recluse spider venom and brown recluse spider toxin, was followed by phosphorous-31 nuclear magnetic resonance spectroscopy. The overall rate of hydrolysis of sphingomyelin in mixed micelles was found to be an order of magnitude faster than the hydrolysis of lysophosphotidylcholine. Incorporation of lysophosphotidylcholine into mixed micelles with Triton X-100 inhibited the lipase activity of brown recluse spider venom and brown recluse spider venom toxin. The effects of increased rates of overall reaction were observed with increased temperature and also with decreased ionic strength. The presence of divalent calcium ions was found to be necessary for hydrolytic activity, but only in catalytic amounts (less than 1 mM).