organization, or government agency to take a certain action. It consists of a systematic mass campaign of telephone calls to the selected target over a period of time.

phosphorylate To introduce the trivalent group =P=O into an organic compound; phosphorylase is any enzyme that in the presence of an inorganic phosphate catalyzes the conversion of glycogen into sugar phosphate. Within the context of HIV/AIDS, it is noted that factors other than viral cross-resistance, such as pharmacological mechanisms, may also be important considerations when planning a long-term strategy. For example, the nucleoside analogs are actually prodrugs that must be converted into their active, triphospherate form by cellular enzymes in the human body. In the late 1990s, research described problems with this process that limit AzT's clinical efficacy. Interest increased in the intracellular phosphorylation of AzT. Two key unknowns at the time were of particular interest: (1) whether not the rate of phos-phorylation decreases after prolonged exposure to a particular drug over time and (2) whether prior use of one compound affects the subsequent ability of the cell to phosphorylate new drugs.

phosphorylation The addition of a phosphate group (phosphorous plus four oxygen atoms) to an organic molecule.

photophoresis A process by which a light-sensitive drug called psoralen is used to treat various autoimmune diseases. The drug is injected into the body; after an interval blood containing psoralen is removed from the body and exposed to ultraviolet light, thus activating the drug in white blood cells. Finally, the blood is returned to the body by reinfusion. The whole procedure is usually performed on two consecutive days at monthly intervals and takes about four hours per session. Photophoresis is an approved therapy for a skin cancer called cutaneous t-cell lymphoma. In the test tube, it has been shown to work to inhibit viruses that involve RNA and DNA including HIV.

photosensitivity Heightened skin response to sunlight or ultraviolet light (rapid burning when exposed to the sun).

PHS See public health service.

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