Phenolphthalein disulfate is used in a broth as a substrate for arylsulfatase. This broth is a medium used to differentiate pathogenic mycobacteria based on their arylsulfatase production ability, those that produce arylsulfatase release phenolphthalein and, with the addition of an alkali, will turn the solution pink. The desulfuration of phenolphthalein disulfate was also used to isolate and identify intestinal bacteria.

Phenyl-alpha-D-glucopyranoside is as reagent used in chemical synthesis. TAS2R16 receptor mediates bitter taste in response to beta-glucopyranosides.

Phenyl-beta-D-glucopyranoside is a substrate for beta-glucosidase.

Phenyl-β-D-galactopyranoside is a noninducing β-galactosidase substrate. It is used in selection of mutants of lacZ plasmid-based transgenic mice. It is an acceptor substrate in fucosyltransferase detection.

PMSF is a serine protease inhibitor that irreversibly inhibits serine proteases by sulfonylation of the serine residue in the active site of the protease. It is widely used in protocols for the isolation of proteins.

PMSF is inactivated in aqueous solutions. The rate of inactivation increases with increasing pH and is faster at 25°C than at 4°C. The half-life of a 20mM aqueous solution of PMSF is ~35 minutes at pH 8.0. This short half-life means that aqueous solutions of PMSF can be safely discarded after they have been rendered alkaline (pH >8.6) and stored for several hours at room temperature.

Phenylpropiolic acid is a reagent used in chemical synthesis. It has been used in the synthesis of tacchykinin receptor antagonists and catalyzation of aryl and vinyl cross-coupling reactions.

Phosphinothricin is a broad-spectrum herbicide that acts as a competitive inhibitor of glutamine synthetase.

Glutamine synthetase plays an important role in plant nitrogen metabolism. Its actions lead to the formation of glutamine; however, when inhibited by phosphinothricin, a rapid accumulation of ammonia along with reduction in glutamine occurs within plants.

This herbicide makes an ideal agent for the selection of transformed plants. Plant resistance to phosphinothricin is conferred through the bar gene, and due to the fast degradation of phosphinothricin in soil and in water, it presents a low risk for environmental contamination.

Phosphoric ac, mono(4-nitrophenyl) ester is a chromogenic substrate used with ELISA and spectrophotometric assays for acid and alkaline phosphatase.

Phytic acid, dodecasodium salt is present in all eukaryotic cells and functions as a phosphate storage depot and precursor to inositol phosphates and pyrophosphates in plant species. It is also a chelator of divalent and trivalent cations and acts with nuclear pore protein Gle1 in yeast. Phytic acid is used to determine zinc bioavailability.