Short communication and preliminary note

In vitro phosphorylation of pyrimidine desocyribosemononucleotides☆

This chapter describes nucleoside diphosphokinase. The term “nucleoside diphosphokinase” (NDP kinase) is used to designate a family of relatively unspecific enzymes that catalyze the transfer of the terminal phosphate group of 5'-triphosphate nucleotides to 5'-diphosphate nucleotides. All NDP kinases that have been examined to date function through the formation of enzyme-bound high-energy phosphate intermediates. In earlier studies, a notable achievement was the crystallization of NDP kinase from Brewer's yeast. Today, the only crystalline preparations of NDP kinase available are those from yeast, although several laboratories have purified NDP kinases from various sources to apparent homogeneity. The only precise studies of the subunit structure, physicochemical properties, amino acid end groups, and composition of an NDP kinase have been performed with a crystalline yeast preparation that has been found to be a homologous hexamer with a monomer of about 17,000 daltons. A recent development of considerable importance to future studies of NDP kinases is the discovery of marked electrophoretic heterogeneity of the enzyme in a number of tissues. In this chapter, molecular and catalytic properties of NDP kinase are described in detail. The functions of this enzyme in the cell are also discussed in the chapter.

The activities of the adenylate kinase (ATP:AMP phosphotransferase, EC 2.7.4.3) isozymes have been determined from the subcellular compartments of several rat tissues. Adenylate kinase isozyme II was the major species in skeletal muscle, heart, diaphragm, brain, lungs, and uterus. It was found in the cytoplasm of these tissues. The predominant isozyme in kidney, liver, and testis was adenylate kinase III. It was located in the mitochondria from these tissues. A direct correlation was observed between the tissue respiratory rate and ratio of adenylate kinase isozymes III/II.