PARTICULATE AND SOLUBLE FORMS OF THE INDUCIBLE NITRIC-OXIDE SYNTHASE ARE DISTINGUISHABLE AT THE AMINO-TERMINUS IN RAW-264.7 MACROPHAGE CELLS

We report here on the characterization of soluble and particulate form s of the inducible nitric oxide synthase in RAW 264.7 macrophage cells . Stimulation of these cells with E. coli lipopolysaccharide and inter feron-gamma resulted in a significant induction of nitric oxide syntha se activity with approximately 20% of the total activity localized to the cell membrane. Like the soluble enzyme form, the membrane-associat ed nitric oxide synthase activity was inhibited by N-G-monomethyl-L-ar ginine and did not require the addition of calcium. Both protein forms were immunoreactive on Western blots with antibodies specifically rec ognizing the carboxyl terminus of the protein. In contrast, antibodies specific for the amino terminus recognized inducible nitric oxide syn thase from the cytosol, but failed to recognize the membrane-associate d protein. Thus, macrophage cells are capable of expressing two forms of the inducible nitric oxide synthase that are definable by an intrac ellular distribution that correlates to antigenic differences at the a mino terminus. (C) 1995 Academic Press, Inc.