The bone formation process is an example of how both time and nature acted harmonically to pave the path for life as we know. The unique association between calcium phosphate (CaP) and collagen in a single building block, gave rise to one of the most remarkable biomaterials that we know. Our aim in this revision is to provide a brief glance at the different organization levels of the bone tissue, by describing the main their main features. We start with a brief discussion regarding the thermodynamic conditions for mineral formation and how living organisms surpass them. Then we present collagen, the major organic component of bone, in the light of its hierarchical organization as well as its association to CaP crystals. The mechanisms that control both mineral formation and the association with the organic phase are further presented, in which cells and other components of the extracellular matrix, such as matrix vesicles and noncollagenous proteins, become agents of bone construction. Finally, we underline the difficulty of studying the complex process of bone mineralization and present liposomes, proteoliposomes, and Langmuir monolayers as biomimetic approaches to this end.

Streptococcus mutans membrane-bound P- and F-type ATPases are responsible for H+ extrusion from the cytoplasm thus keeping intracellular pH appropriate for cell metabolism. Toluene-permeabilized bacterial cells have long been used to study total membrane-bound ATPase activity, and to compare the properties of ATPase in situ with those in membrane-rich fractions. The aim of the present research was to determine if toluene permeabilization can significantly modify the activity of membrane-bound ATPase of both F-type and P-type. ATPase activity was assayed discontinuously by measuring phosphate release from ATP as substrate. Treatment of S. mutans membrane fractions with toluene reduced total ATPase activity by approximately 80% and did not allow differentiation between F- and P-type ATPase activities by use of the standard inhibitors vanadate (3 µM) and oligomycin (4 µg/mL). Transmission electron microscopy shows that, after S. mutans cells permeabilization with toluene, bacterial cell wall and plasma membrane are severely injured, causing cytoplasmic leakage. As a consequence, loss of cell viability and disruption of H+ extrusion were observed. These data suggest that treatment of S. mutans with toluene is an efficient method for cell disruption, but care should be taken in the interpretation of ATPase activity when toluene-permeabilized cells are used, because results may not reflect the real P- and F-type ATPase activities present in intact cell membranes. The mild conditions used for the preparation of membrane fractions may be more suitable to study specific ATPase activity in the presence of biological agents, since this method preserves ATPase selectivity for standard inhibitors.