β subunit affects Na and K affinities of Na/K-ATPase: Na and K affinities of a hybrid Na/K-ATPase composed of insect α and mammalian β subunits.

The affinity for K of silkworm Na/K-ATPase, which is composed of α and β subunits, is remarkably lower than that of mammalian Na/K-ATPase, with a slightly higher affinity for Na. Because the α subunit had more than 70% identity to the mammalian α subunit in the amino acid sequence, whereas the β subunit, a glycosylated protein, had less than 30% identity to the mammalian β subunit, it was suggested that the β subunit was involved in the affinities for Na and K of Na/K-ATPase. To confirm this hypothesis, we examined whether replacing the silkworm β subunit with the mammalian β subunit affected the affinities for Na and K of Na/K-ATPase.

Inhibition of the human secretory pathway Ca, Mn-ATPase1a by 1,3-thiazole derivatives.

The human Golgi/secretory pathway Ca,Mn-ATPase 1 (hSPCA1) transports Ca and Mn into the Golgi lumen. Studies of the biological functions of hSPCA1 are limited by a lack of selective pharmacological tools for SPCA1 inhibition. The aim of this study was therefore to identify compounds that specifically inhibit hSPCA1 activity.

A possible mechanism for low affinity of silkworm Na/K-ATPase for K.

The affinity for K of silkworm nerve Na/K-ATPase is markedly lower than that of mammalian Na/K-ATPase (Homareda 2010). In order to obtain clues on the molecular basis of the difference in K affinities, we cloned cDNAs of silkworm (Bombyx mori) nerve Na/K-ATPase α and β subunits, and analyzed the deduced amino acid sequences. The molecular masses of the α and β subunits were presumed to be 111.

Localization of Na(+)/K(+)-ATPase in silkworm brain: a possible mechanism for protection of Na(+)/K(+)-ATPase from Ca(2+).

In mammalian blood, the Na(+) concentration is higher than the K(+) concentration, whereas in hemolymph of lepidopterous insects, the K(+) concentration is higher than the Na(+) concentration. Na(+)/K(+)-ATPase regulates Na(+) and K(+) concentrations in mammalian blood. Therefore, the absence of Na(+)/K(+)-ATPase in lepidopterous insects might be expected.

Properties of silkworm Na+/K+-ATPase.

The high Na(+) and low K(+) concentrations in mammalian blood are maintained by Na(+)/K(+)-ATPase. In contrast, the K(+) concentration is higher than the Na(+) concentration in the hemolymph of the silkworm Bombyx mori, a Lepidopterous insect. Although Na(+)/K(+)-ATPase, therefore, appears not to be in silkworm, we confirmed the presence of Na(+)/K(+)-ATPase in nerve tissues of silkworm but not in skeletal muscle or the dorsal vessel.

Stimulation of p-nitrophenylphosphatase activity of Na+/K+-ATPase by NaCl with oligomycin or ATP.

It is known that the addition of NaCl with oligomycin or ATP stimulates ouabain-sensitive and K+-dependent p-nitrophenylphosphatase (pNPPase) activity of Na+/K+-ATPase. We investigated the mechanism of the stimulation. The combination of oligomycin and NaCl increased the affinity of pNPPase activity for K+.