Provided is a method of inhibiting protein kinase C zeta/protein kinase M zeta, including contacting a sample containing an isoform of protein kinase C zeta with a compound of formula: referred to as 1-naphthol-3,6,8-trisulphonic acid, or a pharmaceutically acceptable salt thereof. In some embodiments, contacting the sample with the compound does not inhibit protein kinase C iota/lambda. In a specific example, the sample includes neural tissue, the isoform of protein kinase C zeta is protein kinase M zeta, and inhibiting includes reducing kinase activity and further includes diminishing long-term potentiation. In some embodiment, the method includes inhibiting glucose transport. Also provided is a method of affecting memory, including administering the compounds to a mammalian organism.