Protein labeling and modification is a powerful tool for the isolation and analysis of proteins. The ProtOn™ Protein Labeling Kits simplify the attachment of either biotin or fluorescein to antibodies or other proteins. Vector Laboratories offers a variety of reagents and kits for protein labeling allowing for greater flexibility of experimental design. Labeling Reagents Two functional groups on proteins that are often used in protein modification are primary amino groups, present in lysine residues and chain termini, and thiol groups in cysteine residues. The objective for protein modification determines the functional group that is chosen for labeling. Generally, a protein will have many primary amino groups accessible on its surface. Modification of these surface primary amino groups usually does not affect binding or enzymatic activity of the protein. This allows several labels to be covalently attached and subsequently detected and visualized. Thiol groups are usually less abundant and may be involved in structual elements of the protein like disulfide bridges. Modification of thiol groups, on the other hand, may yield insight into protein structure and function. Vector Laboratories offers reagents for the attachment of labels to either primary amino groups or thiol groups along with their corresponding detection reagents. Glycoproteins may also be labeled with biotin hydrazide through their carbohydrate groups. ProtOn™ Protein Labeling Kits The ProtOn™ protein labeling kits are designed for the simple and fast labeling of proteins with biotin or fluorescein. The kits are ideally suited to label antibodies, hormones, or other proteins as well as other macromolecules containing primary amino groups. Labeled proteins can be used in a number of applications, such as immunological assays, fluorescence microscopy, investigation of protein-protein interactions, etc. The ProtOn™ labeling reagents react with primary amines (i.e. lysine residues or terminal amino groups) on the protein forming a stable covalent bond. Each kit contains all the components needed for at least five labeling reactions (up to 1 mg of protein per reaction). Kit components include: Labeling Reagent* Reagent Solvent Reaction Buffer Stop Reagent Gel Filtration Slurry 5 x 1 ml Spin Columns 5 x 2 ml Collection Tubes Agarose Avidin D Slurry** *N-hydroxysuccinimidyl-6-(biotin amido) hexanoate or fluorescein isothiocyanate. **Included in biotin labeling kit only (for measuring degree of biotinylation).     Paraffin embedded human prostate tissue stained using rabbit anti-PSA labeled with the ProtOn™ Biotin Labeling Kit and detected with VECTASTAIN® Elite® ABC Reagent and Vector® DAB substrate.     Paraffin embedded human prostate tissue stained directly with rabbit anti-PSA labeled with the ProtOn™ Fluorescein Labeling Kit and mounted in VECTASHIELD® HardSet™ and PI.