Since author was fascinated by the important functions of calcium (Ca) for the regulation of intracellular metabolism, author has focused the studies on Ca metabolism. A parameter which evaluates bone strength is essential for the study of Ca/bone metabolism and the prevention of osteoporosis. Therefore, a machine for measurement of bone strength was developed. Dual-energy X-ray absorptiometry (DXA: bone densitometer) is used very widely in human studies, and has proved to be safer and more accurate than other techniques. Author carried out DXA to determine whether it is suitable for the measurement of low bone mineral density (BMD) in small animals. The estrogen-deficient model rat produced by ovariectomy and the estrogen- and Ca-deficient model rat produced by ovariectomy and a low Ca diet were also evaluated to clarify whether these animal models were useful as osteoporotic models. For prevention of osteoporosis, it is necessary to take enough Ca and to carry out moderate physical activity. However, Ca intake has never been sufficient in Japan. Therefore, the effects of different Ca sources, other nutrients which affect Ca metabolism and physical activity on bone metabolism were examined. It is well known that a reaching a high peak bone mass at a young age and minimizing bone loss with aging and/or the menopause are also important for prevention of osteoporosis. Therefore, the effects of diet and daily physical activity on the BMD of pre/post menopausal women were investigated using DXA from the viewpoint of osteoporosis prevention.
Branched chain fatty acids (BCFAs) of the iso and anteiso series are synthesized from branched-chain amino acids (BCAAs) in many bacteria and in animal skin. This communication describes the biosynthesis of BCFA in Bacillus subtilis and rat skin. BCFAs of Bacillus subtilis are synthesized from the α-keto acids of BCAAs. Two distinct decarboxylases were present in the crude BCFA synthetase of Bacillus subtilis: branched chain α-keto acid (BCKA) decarbaxylase and pyruvate decarboxylase. BCFA synthetase activity was completely lost upon immunoprecipitation of BCKA decarboxylase, suggesting that this enzyme is essential for BCFA biosynthesis by Bacillus subtilis. A BCKA decarboxylase-mediated mechanism was postulated for BCFA biosynthesis. Supplementation of the diet with valine and isoleucine increased the levels of respective BCFAs in the skin surface lipids of rat. However, this was not the case for leucine. Serum levels of valine, isoleucine and their α-keto acids correlated well with the level of the respective BCFAs in the skin surface lipids. Incorporation in vivo of [14C] -BCAA and BCKA into the skin surface lipids revealed that valine and isoleucine rather than their α-keto acids were used mainly for BCFA biosynthesis by rat skin. BCFA synthesis by rat skin differed from that by bacteria in that the systems did not use leucine as a primer. Leucine was used for biosynthesis of straight-chain fatty acids rather than for BCFAs. Substrate specificity and stereoselectivity in vivo of animal BCFA synthesis was described.