Katsuhiko Takabayashi

Adenosine kinase catalyzes the phosphorylation of adenosine to AMP and hence is a potentially important regulator of extracellular adenosine concentrations. Despite extensive characterization of the kinetic properties of the enzyme, its primary structure has never been elucidated. Full-length cDNA clones encoding catalytically active adenosine kinase were obtained from lymphocyte, placental, and liver cDNA libraries. Corresponding mRNA species of 1.3 and 1.8 kb were noted on Northern blots of all tissues examined and were attributable to alternative polyadenylylation sites at the 3' end of the gene. The encoding protein consists of 345 amino acids with a calculated molecular size of 38.7 kDa and does not contain any sequence similarities to other well-characterized mammalian nucleoside kinases, setting it apart from this family of structurally and functionally related proteins. In contrast, two regions were identified with significant sequence identity to microbial ribokinase and fructokinases and a bacterial inosine/guanosine kinase. Thus, adenosine kinase is a structurally distinct mammalian nucleoside kinase that appears to be akin to sugar kinases of microbial origin.

Abstract It has been anticipated that type C oncornaviruses, which participate in the pathogenesis of murine systemic lupus erythematosus (SLE), would be found to have a role in the development of SLE in humans. In studies of tissues from SLE patients, type C–related proteins have been identified. Using information obtained on the recent isolation of the human T cell leukemia virus (HTLV), together with that from studies of murine SLE, we attempted to clarify the role of antibodies to HTLV in the pathogenesis of human SLE. Using a solid‐phase enzyme‐linked immunosorbent assay and sodium dodecyl sulfate–polyacrylamide gel electrophoretic techniques, we were unable to find evidence of the participation of antibodies to HTLV proteins in the development of human SLE.

The I-J and antigen-binding chains with constant region determinant (Ct) that compose an antigen-specific suppressor T cell factor were found on the surface of suppressor T cell hybridomas, serologically and morphologically demonstrated by a fluorescence-activated cell sorter (FACS) and immunoelectron microscopic analyses. Moreover, the surface expression of the I-J and Ct-bearing chains fluctuating with the same kinetics depended entirely upon the cell cycle. The maximum expression of these two chains was observed in the early stage of the M phase, and the minimum in the S phase. Similarly, the magnitude of the suppressor activity was maximal in the late stage of the M phase, and was minimal in the S phase. The results therefore demonstrated that there exists good correlation between the cell surface expression of the I-J and Ct-bearing chains and the magnitude of the suppressor activity produced. The antigen recognition units on suppressor T cell hybridomas have serologically and morphologically been characterized by using radiolabeled antigens or monoclonal antibodies against the I-J or Ct on the antigen-binding molecule. Cell-binding assay and radioautographic analysis demonstrated that the suppressor T cell hybridoma possesses the capacity to bind native antigen in an antigen-specific fashion as does the hybridoma-derived, antigen-specific suppressor factor composed of the I-J and the Ct-bearing chains, indicating that the recognition unit on the cell surface is composed of a structure similar to the factor.

The crystal structures of specific granules in human eosinophils were studied by thin sectioning and deep-etching with the aid of Fourier transformation. The crystal, thought to be a simple cubic by previous studies by thin sectioning, was demonstrated as the body-centered cubic (the cesium chloride type) consisting of two kinds of particles. The crystal parameters obtained by deep-etching were slightly larger (a = b = c = 4.1-4.4 nm) than by thin sectioning (4.0 nm). By deep-etching, the crystal also showed the stacking folds suggesting the piled-up plates. Although it is known that the patients with hypereosinophilic syndrome have more hypodense eosinophils compared with normal persons, no morphological differences could be detected in the crystals between these eosinophils.