Lysozyme is perhaps the most widely known and best characterized nonimmune antibacterial substance in saliva. Our overall objective is to define the role of lysozyme in the oral cavity. Lysozyme is a strongly cationic protein that possesses bacteriolytic (muramidase) enzymatic activity. Lysozyme has several effects on bacteria including aggregation, disruption of membrane function, death and lysis. Virtually all of these effects can also occur with enzymatically-inactive lysozyme, thus, in the septic environment lysozyme may be the most resilient antibacterial component. The specific aims of the proposed research are (i) to characterize membrane permeability, autolytic and bactericidal effects of native and muramidase- inactive lysozyme on oral bacteria, (ii) to investigate microbe-lysozyme interactions in vivo using immunolocalization of lysozyme in salivary sediment, mucosal coatings and dental plaque, and (iii) TO IDENTIFY NONPEPTIDOGLYCAN BACTERIAL TARGETS OF MURAMIDASE-ACTIVE AND MURAMIDASE- INACTIVE LYSOZYME. Methods of approach include lysozyme adhesion to oral bacteria, viability assays, lysis and autolysis of 3H-DNA labeled bacteria, K+ and PEP permeability of bacterial membranes, bacterial fermentation and glucose uptake, COVALENT CROSSLINKING OF LYSOZYMES TO BACTERIAL TARGET PROTEINS and immunogold detection of lysozyme in oral specimens with electron microscopy. The results of this study will (i) define the range and limits of antibacterial activities of muramidase-inactive lysozyme compared to the native substance and (ii) indicate the extent, nature and perhaps outcomes of lysozyme-microbe interactions in the human mouth. Since several secretions that bathe mucosal surfaces contain lysozyme, the results of this study should be generally applicable to mechanisms of mucosal defense.