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A phosphatidylinositol-cleaving phospholipase C (PI-PLC) activity is released into the extracellular environment by intact Swiss 3T3 cell cultures. The activity is found in both serum-containing and serum-free defined culture medium. The cells remain attached and intact by Trypan Blue exclusion and lactate dehydrogenase assays. The activity is specific for phosphoinositides as no cleavage of phosphatidylcholine is observed. The activity is a phospholipase C rather than D since the water soluble products formed from cleavage of [3H]phosphatidylinositol were inositol phosphates and not inositol. Analysis of the inositol phosphate products showed a variation in composition with the pH of the assay, the ratio of noncyclic:cyclic forms being 60:40 at pH 7.5 and 40:60 at pH 5.5. This external phospholipase C resembles the well-characterized intracellular isozymes in that it is calcium-dependent and has a pH optimum between 5 and 6. From membrane filter assays the molecular weight of the native enzyme is estimated to be between 50 and 100 kDa.
G B Birrell, and
K K Hedberg, and
O H Griffith
February 1993,
Biochimica et biophysica acta,
G B Birrell, and
K K Hedberg, and
O H Griffith
May 1989,
Science (New York, N.Y.),
G B Birrell, and
K K Hedberg, and
O H Griffith
June 1992,
The Journal of biological chemistry,
G B Birrell, and
K K Hedberg, and
O H Griffith
September 1990,
FEBS letters,
G B Birrell, and
K K Hedberg, and
O H Griffith
August 1994,
Seikagaku. The Journal of Japanese Biochemical Society,
G B Birrell, and
K K Hedberg, and
O H Griffith
December 1987,
Journal of neurochemistry,
G B Birrell, and
K K Hedberg, and
O H Griffith
July 1989,
European journal of biochemistry,
G B Birrell, and
K K Hedberg, and
O H Griffith
January 1999,
Journal of biomolecular screening,
G B Birrell, and
K K Hedberg, and
O H Griffith
December 1987,
Molecular immunology,
G B Birrell, and
K K Hedberg, and
O H Griffith
September 2002,
Plant physiology,
