Structure and function of muscle myosin

We have studied the primary structures of myosins from chicken muscles in order to clarify the relationship between structure and function of muscle myosin. The primary structures of the various kinds of light chains from chicken muscle myosins have been determined. We also report the primary structure of the 23K fragment of subfragment-1 (S-1) component from the heavy chain of chicken fast skeletal muscle myosin. In addition, antibody was prepared against the 23K fragment. The antibody was found to inhibit the Mg²⁺-ATPase activity and the initial P_i burst of the ATPase in the S-1 component. The antibody suppressed the ATP-induced fluorescence enhancement of S-1, though it did not suppress the binding of ATP to S-1. These results are also discussed.This article was presented during the proceedings of the International Conference on Macromolecular Structure and Function, held at the National Defence Medical College, Tokorozawa, Japan, December 1985.     

Anti-parasite activity of nucleoside analogues: the metabolism of carbocyclic inosine in promastigotes of Leishmania tropica and Leishmania donovani and its activity against amastigotes of Leishmania donovani in vitro

Carbocyclic inosine is a potent inhibitor for the growth of the promastigote form of Leishmania tropica and Leishmania donovani. In culture, the EC50 values of carbocyclic inosine are 8.3 X 10(-8) and 1.3 X 10(-7) M for the promastigotes of L. tropica and L. donovani, respectively. On the other hand, it is less toxic towards mouse mammary tumor FM3A cells: the EC50 value is 2.7 X 10(-4)M. Carbocyclic inosine is metabolized by Leishmania promastigotes to give carbocyclic adenosine-5'-triphosphate(aristeromycin-5'-triphosphate) and carbocyclic guanosine-5'-triphosphate. This metabolic conversion provides a mechanism for the parasite-selective toxicity of carbocyclic inosine. Carbocyclic inosine was found to be active against L. donovani amastigotes in an in vivo-like cultivation in vitro.     

Skill-Specific Changes in Somatosensory Nogo Potentials in Baseball Players

Athletic training is known to induce neuroplastic alterations in specific somatosensory circuits, which are reflected by changes in somatosensory evoked potentials and event-related potentials. The aim of this study was to clarify whether specific athletic training also affects somatosensory Nogo potentials related to the inhibition of movements. The Nogo potentials were recorded at nine cortical electrode positions (Fz, Cz, Pz, F3, F4, C3, C4, P3 and P4) in 12 baseball players (baseball group) and in 12 athletes in sports, such as track and field events and swimming, that do not require response inhibition, such as batting for training or performance (sports group). The Nogo potentials and Go/Nogo reaction times (Go/Nogo RTs) were measured under a somatosensory Go/Nogo paradigm in which subjects were instructed to rapidly push a button in response to stimulus presentation. The Nogo potentials were obtained by subtracting the Go trial from the Nogo trial. The peak Nogo-N2 was significantly shorter in the baseball group than that in the sports group. In addition, the amplitude of Nogo-N2 in the frontal area was significantly larger in the baseball group than that in the sports group. There was a significant positive correlation between the latency of Nogo-N2 and Go/Nogo RT. Moreover, there were significant correlations between the Go/Nogo RT and both the amplitude of Nogo-N2 and Nogo-P3 (i.e., amplitude of the Nogo-potentials increases with shorter RT). Specific athletic training regimens may induce neuroplastic alterations in sensorimotor inhibitory processes.     

SOCS2 Balances Metabolic and Restorative Requirements during Liver Regeneration

After significant injury, the liver must maintain homeostasis during the regenerative process. We hypothesized the existence of mechanisms to limit hepatocyte proliferation after injury to maintain metabolic and synthetic function. A screen for candidates revealed suppressor of cytokine signaling 2 (SOCS2), an inhibitor of growth hormone (GH) signaling, was strongly induced after partial hepatectomy. Using genetic deletion and administration of various factors we investigated the role of SOCS2 during liver regeneration. SOCS2 preserves liver function by restraining the first round of hepatocyte proliferation after partial hepatectomy by preventing increases in growth hormone receptor (GHR) via ubiquitination, suppressing GH pathway activity. At later times, SOCS2 enhances hepatocyte proliferation by modulating a decrease in serum insulin-like growth factor 1 (IGF-1) that allows GH release from the pituitary. SOCS2, therefore, plays a dual role in modulating the rate of hepatocyte proliferation. In particular, this is the first demonstration of an endogenous mechanism to limit hepatocyte proliferation after injury.     

The amino acid compositions of the tryptic, chymotryptic and peptic peptides from the L-2 light chain of rabbit skeletal muscle myosin.

The light chain fraction was separated from rabbit skeletal muscle myosin and four kinds of light chains, L-1, L-2, L-3 and L-4 in the fraction were further isolated by column chromatography using DEAE-cellulose DE-52. After amino-ethylation, the L-2 light chain was digested with trypsin. It was also digested with chymotrypsin and pepsin, respectively, after carboxymethylation. Each of the tryptic, chymotryptic and peptic peptides thus obtained was separated and purified and their amino acid compositions were analyzed.     

Detection of T-cell surface determinants in three Marek's disease lymphoblastoid cell lines.

The T-cell surface antigens on three lymphoblastoid cell lines, MOB1, MOB-2 and MSB-1, derived from Marek's disease lymphomas were examined by the cytotoxicity test and the indirect membrane immunofluorescent test. These cell lines reacted specifically with antisera prepared against chicken thymus cells, although their reactivities were less than that of typical thymus cells. These three cell lines were of thymus origin.