Current Topics in Cellular Regulation: Volume 23 is a collection of papers that discusses pyruvate carboxylase, the regulation of carbohydrate metabolism, and the plasma membrane ATPase of fungi or plants. Other papers deal with adrenergic control of phosphofructokinase, protein phosphatase, as well as the regulation of polypeptide precursors of mature mitochondrial proteins. One paper explains the three dimensional structure of pyruvate carboxylase and its reaction mechanism. Electron microscopic analyses show that four monomers of pyruvate carboxylases isolated from vertebrate sources form a tight tetrahedron-like structure. Another paper describes the regulation of fructose 2,6-bisphosphate concentration in the liver and of the enzymes that are responsible for its metabolism, and the mechanism involved in fructose, particularly in the regulation of 6-phosphofructo-1-kinase and fructose-1,6-bisphosphatase activity. The paper also explains the role of this effector in the regulation of hepatic carbohydrate metabolism. One paper deals with the different levels of biological organization (whole cells, isolated plasma membranes, and purified enzyme) that characterizes the plasma membrane ATPase of fungi and plants as a novel type of proton pump. The collection can prove useful for biologists, microbiologists, students, and professors of biology and biophysics.