PubMed · 4496324
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1972. Fluocinonide.. https://pubmed.ncbi.nlm.nih.gov/4496324/
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The crystals of beta-amylase from Bacillus cereus belong to space group P21 with the following cell dimensions: a = 57.70 A, b = 92.87 A, c = 65.93 A, and beta =101.95 degrees. The structures of free and maltose-bound beta-amylases were determined by X-ray crystallography at 2.1 and 2.5 A with R-factors of 0.170 and 0.164, respectively. The final model of the maltose-bound form comprises 516 amino acid residues, four maltose molecules, 275 water molecules, one Ca2+, one acetate, and one sulfate ion. The enzyme consists of a core (beta/alpha)8-barrel domain (residues 5-434) and a C-terminal starch-binding domain (residues 435-613). Besides the active site in the core where two maltose molecules are bound in tandem, two novel maltose-binding sites were found in the core L4 region and in the C-terminal domain. The structure of the core domain is similar to that of soybean beta-amylase except for the L4 maltose-binding site, whereas the C-terminal domain has the same secondary structure as domain E of cyclodextrin glucosyltransferase. These two maltose-binding sites are 32-36 A apart from the active site. These results indicate that the ability of B. cereus beta-amylase to digest raw starch can be attributed to the additional two maltose-binding sites.
In probing the possible non-genotoxic molecular mechanism(s) of nickel(II)-induced carcinogenesis, we performed a non-radioactive mRNA differential display analysis for nickel(II) acetate-treated Chinese hamster ovary cells (CHO-K1-BH4). Three out of thirty differentially expressed cDNAs had sequences highly similar to known genes. Down-regulation of vimentin and a hSNF2H homologue and up-regulation of ferritin heavy chain were confirmed by Northern blot analysis. The expression of these mRNAs was time- and nickel(II) concentration-dependent. For vimentin, the decrease in mRNA level was concurrent with a decrease in the protein level. For ferritin, the increase in mRNA had no effect on the protein level. Dysregulation of these gene products signifies their involvement in the epigenetic effects of carcinogenic nickel(II) compounds.
The binding of chloride and acetate to photosystem II (PSII) was examined to elucidate the mechanism of acetate inhibition. The mode of inhibition was studied, and individual binding sites were assigned by steady-state O2 evolution measurements in correlation with electron paramagnetic resonance (EPR) results. Two binding sites were found for acetate, one chloride-sensitive on the electron donor side and one chloride-insensitive on the electron acceptor side. The respective binding constants were as follows: KCl = 0.5 +/- 0.2 mM (chloride binding to the donor side), KI = 16 +/- 5 mM (acetate binding to the donor side), and KI' = 130 +/- 40 mM (acetate binding to the acceptor side). When acetate was bound to the acceptor side of PSII, 200 K illumination induced a narrowed form of the QA-FeII EPR signal, the yield of which was independent of the chloride concentration. When acetate was bound to the donor side, room-temperature illumination produced the S2YZ* state. EPR measurements showed that both the yield and formation rate of this state increased with acetate concentration. Increasing chloride concentrations slowed the rate of formation of the S2YZ* state, but did not affect the steady-state yield of the S2YZ* state. These findings indicate that the light-induced reactions in acetate-inhibited PSII are modulated by both donor side and acceptor side binding of acetate, while the steady-state yield of the S2YZ* state at the high PSII concentrations used for EPR measurements depends primarily on acceptor side turnover. Our data further support a close proximity of chloride to YZ*, indicating a possible role for chloride in the electron-transfer mechanism at the O2-evolving complex.