Modulation of protein kinase C activity by palmitoyl esters of maltose

Mixtures of maltose palmitates containing predominantly maltose tetrapalmitate (designated MTP) possess immune potentiating and antitumor properties. Immune potentiation derives from macrophage activation and B lymphocyte mitogenicity and antitumor action from anti-angiogenic activity. Their mode of action at the cellular level is not known. Since high performance liquid chromatography (HPLC) provided purified maltose palmitates, we tested whether they individually and as a mixture could modulate activity of protein Kinase C (PKC), an enzyme implicated in mitogenic and release reactions. MTP activated crude lymphocyte and purified brain PKC in the absence of phosphatidyl serine (PS). It also augmented labeled dibutyryl phorbol (PDBu) binding to the brain enzyme in the absence of phospholipid. HPLC purified maltose tetrapalmitates (two isomers) were insoluble in aqueous solvent, and activated PKC slightly after incorporation into PS liposomes. Purified maltose di- and tri-palmitates were inhibitory to the enzyme. The activation of PKC was, therefore, due to higher saturated maltose palmitates, well dispersed by less substituted maltose palmitates acting as emulsifiers.