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201.
T. OConnor S. Mansy M. Bina D.R. McMillin M.A. Bruck R.S. Tobias 《Biophysical chemistry》1982,15(1):53-64
The pH-dependent structure of calf thymus DNA is analyzed using Raman spectroscopy. The Raman spectra in the acidic region demonstrate that denaturation occurs in several steps. The binding of H+ to adenine and cytosine residues is accompanied by a decrease in the percentage of DNA in the B-conformation and a concurrent increase in a conformation most probably related to the C-form. The denaturation of DNA is observed at pH 3.3 and parallels the protonation of guanine bases. The Raman spectra of calf thymus DNA in the basic region (above pH 10) show that guanine residues are deprotonated at a lower pH value than are thymine residues. In addition, Raman spectra in the basic region detect conformational changes of the phosphate backbone different from those found in the acidic region. 相似文献
202.
Fungi produce and accumulate various carotenoids. Mycelia of the ZygomyceteBlakeslea trispora contained β-carotene and its precursors γ-carotene and lycopene. When strains of opposite sex grew together, the β-carotene
concentration increased fourfold, that of γ-carotene remained unchanged, and other intermediates practically disappeared.
The inhibitors nicotine, 2-(4-chlorophenylthio)-triethylamine, α-picoline, and imidazole increased the concentrations of lycopene
and γ-carotene and decreased those of β-carotene. From our quantitative results, we conclude thatBlakeslea has two pathways for lycopene metabolism, of which other fungi have only one or the other. The main one, two cyclizations
from lycopene to β-carotene, is carried out by an enzyme dimer, is stimulated by sexual interaction, and is sensitive to the
inhibitors. The other pathway, a cyclization to γ-carotene is not affected by mating or the inhibitors. 相似文献