The binding sites of cytochalasin D. II. Their relationship to hexose transport and to cytochalasin B

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Abstract
Cytochalasin B (CB) was able to compete with tritiated cytochalasin D (3H‐CD) for binding sites in HEp‐2 cells. The pattern of inhibition suggested that CB associates with a low affinity class of CD binding sites. Glucose and maltose did not inhibit binding of 3H‐CD to isolated HEp‐2 plasma membrane. Inhibition of hexose transport by CD was negligible, but CD did not block the potent inhibition of this transport by CB. These results indicate that CD does not bind to the high affinity CB receptor reportedly associated with the hexose transport system, and that this receptor cannot mediate the morphological effects of CD. Both CD and CB induced contraction‐zeoisis in HEp‐2 cells; CB was less potent than CD, and their effects appeared to be additive. It was concluded that the high affinity binding sites for CD and CB are different, but that these congeners share a low affinity site. Both high and low affinity sites for CD appear to mediate its morphological effects; only the low affinity class appears to be involved for CB. Possible identification of the common low affinity binding site as actomyosin (detailed in Tannenbaum et al., 1977) is further discussed.