Biochimica et biophysica acta最新文献

All the details concerning the establishment of the formula of the chemical structure of hen's egg-white lysozyme (N-acetylmuramide glycanohydrolase, EC 3.2.1.17) (which the authors had briefly indicated in 1961) are reported in the present study. The 18 tryptic units obtained from reduced lysozyme by chromatography on Dowex-1 X2 have beeb joined in the right order thanks to the chymotryptic units containing a basic amino acid and in two instances thanks to the peptic units. The protein is formed by a single polypeptide chain of 129 amino acid residues folded by the 4 bridges of the cystine residues; one of them has already been determined. Some considerations are made on the relations existing between chemical structure and biological activity.

The effect of 8% dioxane on the optical rotatory dispersion of myosin A purified by treatment with DEAE-cellulose was measured in 0.6 M KCl and at pH 7.0 and 20°. The increase in the —b₀ term by 5% was followed by a gradual decrease to 0.88 of the original. The —b₀ term of L₁-meromyosin in 0.6 M KCl and at pH 7.0 and 20% was 575 and was unchanged by the addition of dioxane, ATP of PP₁. On the other hand, the —b₀ term of H₂-meromyosin in 0.3 M KCl and at pH 7.0 and 20% was 263. It increased by several percent immediately after the addition of 8% dioxane and decreased gradually with time. It increased by several percent on the addition of 4 moles p-chloromercuribenzoate, but decreased by several percent on the addition of 8 moles p-chloromercuribenzoate per 10⁵ g protein. It was also decreased by the binding of H₂-meromyosin with F-actin. ATP increased the —b₀ term of H₂-meromyosin by several percent, though PP₁ decreased the term by several percent. Thus these reagents change the helical content of H₂-meromyosin in ways similar to the case of myosin A. The extents of the changes in the helical content of H₂-meromyosin by F-actin and ATP were, however, higher than those observed in myosin A.

The following sequence of metabolic reactions has been proved by chemical methods to occur in resting cells of acid-fast bacteria: p-aminobenzoic acid → p-aminobenzyl alcohol → p-hydroxyaniline. The first step in this sequence has been demonstrated to be a direct enzymatic reduction by using both ring- and carboxy-¹⁴C-labeled p-aminobenzoic acid. A synthetic route, which should be of general use, was employed to convert [¹⁴C]aniline to ring-¹⁴C-labeled p-aminobenzoic acid. It is suggested that the unique transformation of p-aminobenzyl alcohol to p-hydroxyaniline may be a specific case of a more general mechanism involved in enzymatic hydroxylation of aryl compounds.

An enzyme, transferring the acetyl group of N-α-acetylornithine to the amino group of glutamate, has been demonstrated for Saccharomyces cerevisiae. On the other hand, the enzymic reduction of N-α-acetylglutamate with the formation of N-α-acetyl-glutamic-γ-semialdehyde has been reported previously. The absence of transacetylase in an arginine-requiring mutant (gene ar₇) as well as the above findings prove that:

• 1.

  1. The biosynthesis of ornithine, in yeast, proceeds through acetylated intermediates.

• 2.

  2. The transacetylase is the only functional pathway for the conversion of N-α-acetylornithine to ornithine, in spite of the simultaneous presence of an N-α-acetylornithinase (N-α-acetylornithine amidohydrolase).

At least two steps in the biosynthesis of ornithine are repressible by arginine.

Changes in free and acetylated amino acids have been determined in control and infected tobacco plants during logarithmic tobacco mosaic virus multiplication. An increase in free amino acids occurs in infected tissue in the early stages of tobacco mosaic virus synthesis (72 and 144 h) followed by a decrease after 216 h. Acetylamino acids are not present in infected or in normal plant tissue in amounts that exceed 0.2 μmoles per 100 g of plant tissue. The induction of serine acetylase (acetyl-CoA: L-serine N-acetyltransferase) could not be demonstrated during logarithmic tobacco mosaic virus biosynthesis.

Ascorbic acid has been found to induce the fluorescence of an intermediate oxidation product of noradrenaline which is formed in a ferricyanide oxidation. The fluorescence of the product is a function of the ascorbic acid and noradrenaline concentration and at conditions at which the fluorescence of the noradrenaline product is optimal the fluorescence of adrenaline, tested similarly, in negligible. The reaction has a definite pH optimum (pH 6) and the fluorescence of the final product depends on the time of the oxidation. The stability and rate of formation of the noradrenaline product is dependent upon the concentration level of the ascorbic acid and ferricyanide. The reaction shows promise as the basis for a new noradrenaline assay.