prodrug A modified version or precursor of a parent compound designed to enhance delivery properties and be converted to the parent compound in the body.

product-related impurities Molecular variants of the desired product (e.g., precursors, certain degradation product arising during manufacture and/or storage) that do not have properties comparable to those of the desired product with respect to activity, efficacy, and safety. [From ICH Q6B]

product-related substances Molecular variants of the desired product formed during manufacture and/or stage that are active and have no deleterious effect on the safety and efficacy of the drug product. These variants possess properties comparable to the desired product and are not considered impurities. [From ICH Q6B]

product variant A molecule that is related to the product but differs from it chemically, such as a degradation product, intermediate, or different configuration of the protein of interest due to deamidation or other chemical reactions.

prokaryotes Simple organisms, such as bacteria, with no cell nuclei and only a few cell organelles.

protease An enzyme that cleaves the peptide bonds linking amino acids in protein molecules, classified according to the most prominent functional molecular group (such as serine or cysteine) at the active site; also called proteinase.

proteinase K A serine protease (used in molecular cloning and DNA sequencing, nucleic acid research, and protein and peptide structural analysis) with broad specificity toward aliphatic, aromatic, and other hydrophobic amino acids, cleaving their peptide bonds.

protein conformation The characteristic three-dimensional shape of a protein, including the secondary, tertiary, and quaternary structure of the peptide chain.

protein folding A rapid biochemical reaction involved in the formation of proteins. It begins even before a protein has been completely synthesized and proceeds through discrete intermediates (primary, secondary, and tertiary structures) before the final structure (quaternary structure) is developed.

protein truncation Shortening a polymeric chain of amino acids; the protein truncation test developed by Dutch researchers screens proteins to identify abnormally short molecules that suggest the location of genetic mutations.

protein variants Proteins with the same amino acid sequences but different folds or different carbohydrate residues. They must be separated from the therapeutic proteins.

proteins Complex organic macromolecules whose structures are coded in an organism's DNA. Each is a chain of more than 40 amino acids in peptide linkages that folds back upon itself in a particular way. Proteins are the principal constituent of all cell protoplasms (the entire contents of a live cell). Each protein has a unique, genetically defined amino acid sequence that determines its specific shape and function (as enzymes, structural elements, hormones, and immunoglobulins, involved in oxygen transport, muscle contraction, or electron transport, for instance).

proteolysis Separation (cleavage) of peptide bonds in proteins by proteases (enzymes that recognize and cut specific peptide bonds) or other means.

proteolytic Capable of lysing (denaturing, or breaking down) proteins.

proteome The complete listing and description of all the proteins and their functions for an organism.

proteomics Study of protein function and structure.

protocols Documentation (submitted to FDA or other agency in support of regulatory filings) that directs the work performed in an FDA-regulated company. Protocols tell who directs which activities, who approves what, and who is allowed to sign off on materials and products, even where to find specific files and documents—all tying together numerous SOPs.