The kinetics of the reduction of isocyanides, acetylenes and the cyanide ion by nitrogenase preparation from Azotobacter chroococcum and the effects of inhibitors

1. Nitrogen-fixing preparations from Azotobacter chroococcum reduced substrates with the following K(m) values: methyl isocyanide, 1.8x10(-4)m; ethyl isocyanide, 2.5x10(-2)m; cyanide ion, 1.4x10(-3)m; acetylene, 1.2x10(-4)m. 2. Nitrogen, carbon monoxide or hydrogen competitively inhibited isocyanide reduction with the following K(i) values: hydrogen, 1.3x10(-3)m; carbon monoxide, 6.8x10(-6)m; nitrogen, 4.3x10(-4)m. 3. Living nitrogen-fixing bacteria, and isolated clover nodules, formed methane from methyl isocyanide. 4. These results are discussed in relation to other work and possible mechanisms of nitrogen fixation.

STUDIES ON BONE MATRIX IN NORMAL AND OSTEOPOROTIC BONE

1. The appearance of decalcified bone matrix in the electron microscope is described.

2. In the matrix two types of collagen fibril have been distinguished. Differences observed are in solubility, x-ray diffraction pattern and appearance. In infant bone the form which appears as fine fibrils predominates. In adult bone the form which appears as tubular fibrils of larger diameter predominates.

3. In bones from elderly subjects the chemical reaction employed to convert collagen into eucollagen sometimes hydrolyses fatty acid esters, and lines due to the free fatty acid are found on the x-ray diffraction patterns of the insoluble residue after citrate extraction.

4. In ancient bones and fossils the stable tubular form of collagen survives, but not the fine fibrils.

5. When decalcified, the matrix in osteoporotic bones loses its architecture and fibrillar form. Under conditions in which only a small fraction is dissolved from normal bone most of the collagen in osteoporotic bone disperses in citric acid. The insoluble residue then gives a modified x-ray diffraction pattern.

6. Evidence has been produced to suggest that the immediate cause of many forms of osteoporosis is some local factor affecting the osteocytes, rather than a general chemical effect.