48 teeth of chiton form on what is essentially a

Info icon This preview shows pages 38–40. Sign up to view the full content.

View Full Document Right Arrow Icon
48 Teeth of chiton form on what is essentially a continually moving belt, in which new teeth are being grown and moved forward to replace mature teeth that have been abraded. How- ever, the study of the mechanisms of biomineralization in general is relatively recent; a great deal of the information currently available, whether about iron in ferritin or about calcium in bone, is somewhat descriptive. Three different forms of biological iron oxides appear to have distinct rela- tionships to the proteins, lipids, or carbohydrates associated with their formation and with the degree of crystallinity. 49 Magnetite, on the one hand, often forms almost perfect crystals inside lipid vesicles of magneto-bacteria. 50 Ferrihydrite,
Image of page 38

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
II. BIOLOGICAL SYSTEMS OF METAL STORAGE, TRANSPORT, AND MINERALIZATION 31 on the other hand, exists as large single crystals, or collections of small crystals, inside the protein coat of ferritin; however, iron oxides in some ferritins that have large amounts of phosphate are very disordered. Finally, goethite [a- FeO(OH)] and lepidocrocite [y-FeO(OH)] form as small single crystals in a complex matrix of carbohydrate and protein in the teeth of some shellfish (lim- pets and chitons); magnetite is also found in the lepidocrocite-containing teeth. The differences in the iron-oxide structures reflect differences in some or all of the following conditions during formation of the mineral: nature of co-precipi- tating ions, organic substrates or organic boundaries, surface defects, inhibitors, pH, and temperature. Magnetite can form in both lipid and protein/carbohydrate environments, and can sometimes be derived from amorphous or semicrystalline ferrihydrite-like material (ferritin). However, the precise relationship between the structure of the organic phase and that of the inorganic phase has yet to be discovered. When the goal of understanding how the shape and structure of biominerals is achieved, both intellectual satisfaction and practical commercial and medical information will be provided. Synthetic iron complexes have provided models for two stages of ferritin iron storage and biomineralization: 51-59 (1) the early stages, when small num- bers of clustered iron atoms are bound to the ferritin protein coat, and (2) the final stages, where the bulk iron is a mineral with relatively few contacts to the protein coat. In addition, models have begun to be examined for the microen- vironment inside the protein coat. 54 Among the models for the early or nucleation stage of iron-core formation are the binuclear Fe(III) complexes with [Fe20(02CR2)]2+ cores;55,56 the three other Fe(III) ligands are N. The JL-oxo complexes, which are particularly accu- rate models for the binuclear iron centers in hemerythrin, purple acid phospha- tases, and, possibly, ribonucleotide reductases, may also serve as models for ferritin, since an apparently transient Fe(II)-O-Fe(III) complex was detected dur- ing the reconstitution of ferritin from protein coats and Fe(II). The facile ex- change of (02CR) for (02PR) in the binuclear complex is
Image of page 39
Image of page 40
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern