Cleavage of scHGF/SF by olfactory bulb extract is inhibited by preincubation with antibodies to tPA. Iodinated HGF/SF was subjected to treatment with olfactory bulb homogenate that had been preincubated with either polyclonal antibodies against murine tPA or a like amount of control IgG preparation. A, Autoradiogram showing inhibition of scHGF/SF cleavage by tPA antibodies. Lane 1, HGF/SF incubated in the absence of olfactory bulb homogenate. Lane 2, HGF/SF incubated in the presence of olfactory bulb homogenate. Lane 3, HGF/SF incubated with olfactory bulb homogenate that was preincubated with tPA antibodies.Lane 4, HGF/SF incubated with olfactory bulb homogenate that was preincubated with a control IgG. sc,hc, and lc refer to the single chain, heavy chain, and light chains of HGF/SF, respectively. The molecular weights in kilodaltons of protein standards are as indicated on theright. B, Histogram depicting mean values ± SE (n = 4) for several scHGF/SF cleavage experiments similar to the one shown in A. Iodinated scHGF/SF was incubated with olfactory bulb extract that had been pretreated with either antibodies against tPA (+Ab) or the same amount of a nonspecific IgG preparation (control) for a period of time determined to give an ∼50% decrease in the scHGF/SF band in the absence of antibody treatment (−Ab). The value obtained from an scHGF/SF band from a mock incubation was set at 100% and used to determine the percent scHGF/SF remaining in the sample.