Characterization of a β-glucosidase from Glycine max which hydrolyses coniferin and syringin

A β-glucosidase which rapidly hydrolyses the cinnamyl alcohol glucosides coniferin and syringin has been purified from cell cultures, hypocotyls and roots of Glycine max. Isoelectric focusing in a column separated the enzyme from several other β-glucosidases which were inactive against either substrate. Syringin and coniferin were the best substrates tested. Both exhibited identical V_max values, whereas the K_m of coniferin (0.6 mM) was twice that of syringin (0.3 mM). The widely used synthetic substrates 4-nitrophenyl-β-glucoside and 4-methyl-umbelliferyl-β-glucoside were poorly utilized. Glucono-1,5-lactone was an effective competitive inhibitor with a K_i of 0.01 mM. From the observed-substráte specificity, a role in the lignification process of higher plants may be predicted for this β-glucosidase.     

Fatty acid composition and lipid synthesis in developing safflower seeds

Linoleic acid predominated in every lipid class during the whole period of seed development of safflower, while linolenic acid decreased with increasing maturation and it was not detected in mature seeds. Just before the initiation of triacylglycerol accumulation, the fatty acid composition of triacylglycerols changed more rapidly than those of phospholipids and glycolipids. Saturated fatty acids tended to accumulate at the 1- and 3-positions of the glycerol molecule and the more highly unsaturated acids at the 2-position. The fatty acid compositions at the 1- and 3-positions were similar in all cases investigated, but in none of the triacylglycerols was the distribution completely symmetrical. The positional distribution of linolenic acid in triacylglycerols prepared from the immature seeds 2 days after flowering and from the leaves was unusual; in spite of its highest degree of unsaturation, it was preferentially esterified at the 1- and 3-positions. When triacylglycerol was most rapidly accumulated (14–18 days after flowering), the incorporation of acetate-[U- ¹⁴C] into total lipids was also maximum and dienoic fatty acids were the principal acids labelled. Diacylglycerols and compound lipids reached the highest rate of synthesis 15 days after flowering, and then a maximum incorporation into triacylglycerol occurred 18 days after flowering. Incubation temperature affected the synthesis of individual lipid classes. Triacylglycerol was more rapidly synthesized at 32° than at 10°, while diacylglycerols and compound lipids were accumulated under the low-temperature condition. A rise of incubation temperature caused a depression in dienoic acid synthesis.     

Biosynthesis of cytokinins by potato cell cultures

Potato cells grown in liquid culture incorporated mevalonic acid lactone-[2-¹⁴C] into free cytokinin (zeatin riboside and zeatin and the cytokinin of RNA (zeatin riboside). The cytokinin liberated by catabolism of RNA can account for no more than 40% of the free cytokinins.     

Chemogenetic evidence supporting multiple allele control of the biosynthesis of (−)-menthone and (+)-isomenthone stereoisomers in Mentha species

The essential oils of certain Mentha species and chemotypes have proportions of (?)-menthone and (+)-isomenthone which differ but show a high degree of heritability in clonal propagation. Oil from an F₂ individual (69–296), selected from numerous 4n M. longifolia (4n = 48) × M. crispa (2n = 48) hybrids for high isomenthone content, had 41.3% isomenthone; the associated but seldom observed alcohols, 1.6% isomenthol, 10.3% neoiso-menthol; and 13% of their esters; in contrast to 8% menthone with 0.1% menthol, 5.0% neo-menthol, and 1.7% esters. Self-pollination of strain 69–296 gave a 3:1 ratio of high isomenthone: high menthone. Crosses with a true breeding high menthone plant having 80% menthone and 3.2% isomenthone gave a 1:1 ratio of the parental phenotypes by GLC analyses and herbage odor. This and data from high isomenthone and high menthone crosses with tester strains lead us to postulate the involvement of a single locus having multiple alleles with true breeding menthone having the genotype P^s P^s, true breeding isomenthone P^r P^r, 69–296 P^r P^s, and high pulegone pp. The P^r allele is not completely dominant over the P^s allele in 69–296 as about 18% of the total ketone derived from pulegone is menthone. Both are dominant over the recessive allele p that largely prevents menthone development. The quantitative amounts of the two isomers are believed to be controlled by the six combinations of the three alleles in a diploid species with graded effects obtained in the more complex genotypes possible in double diploid and octoploid species. 69–296 has (?)-piperitone even though (+)-piperitone is believed to be the common isomer in Mentha.     

Asymmetric incorporation of 4-(2′-carboxyphenyl)-4-oxobutyrate into phylloquinone by Zea mays

Radioactivity from 4-(2′-carboxyphenyl)-4-oxobutyrate-[2-¹⁴C] and 4-(2′-carboxyphenyl)- 4-oxobutyrate-[3-¹⁴C] was incorporated into C-3 and C-2 respectively of phylloquinone in maize shoots. These results show that this substrate is incorporated in the same asymmetric manner into phylloquinone as it is into the bacterial menaquinones.     

Biosynthesis of polyamines in Euglena gracilis

In Euglena gracilis Z the biosynthesis of spermidine and spermine closely resembles the pathways occurring in mammalian tissues and in most microorganisms. l-Ornithine and not l-arginine, as is the case in most plants, is the main precursor of putrescine, and S-adenosylmethionine donates the propylamino moiety for the biosynthesis of spermidine and spermine. Cell-free extracts of Euglena synthesized sym-norspermidine and sym-norspermine from 1,3-diaminopropane and labelled S-adenosylmenthionine. The synthases for the biosynthesis of these two polyamines have a pH optimum of 7.6, like that of spermidine and spermine synthases. Ion exchange chromatography showed two peaks corresponding to the retention times of 2,4-diaminobutyric acid and 1,3-diaminopropane, lower homologues of ornithine and putrescine, respectively. Experiments with dl-2,4-diaminobutyric acid-[4-¹⁴C] did not result in significant incorporation of the label into 1,3-diaminopropane.     

Precocenes as pro-allatocidins in adult female Diploptera punctata: A functional and ultrastructural study

Adult mated females of the viviparous cockroach Diploptera punctata are moderately sensitive to precocenes. Oöcyte growth is inhibited and oviposition is delayed in insects topically treated with precocene II or precocene III. C₁₆ juvenile hormone release by corpora allata of precocene-treated insects is markedly inhibited when compared to corpora allata of acetone-treated controls. Electron microscopy of the corpora allata reveals that precocene treatment results in a disorganisation of the intracellular organelles. Topically applied precocene II reaches a high concentration in the haemolymph (0.5 mM 2 hr after topical application of 250 μg). C₁₆ juvenile hormone release by isolated corpora allata is inhibited by precocenes in vitro; half-maximal inhibition over a 3 hr period is obtained at 0.4 mM precocene II. In vitro inhibition of corpora allata by precocene II concentrations higher than 1 mM rapidly destroys the glands as evidenced by electron microscopy (total disintegration of cellular organelles) and by the virtual cessation of C₁₆ juvenile hormone synthesis by the corpora allata. Inhibition of C₁₆ juvenile hormone release by precocene is time-dependent and is not reversible over the short-term incubation in vitro. This inhibition does not appear to be related to the spontaneous activity of the glands in vitro, and it can be reduced by two epoxidase inhibitors. Precocenes are pro-allatocidins in this species: they are bioactivated within the corpora allata to cytotoxic epoxides.     

The effect of exogenous gibberellic acid on gibberellin biosynthesis by Gibberella fujikuroi

The addition of gibberellic acid and some other gibberellins to cultures of Gibberella fujikuroi suppresses the incorporation of [2-¹⁴C]MVA and ¹⁴C-labelled ent-kaurene into the gibberellin metabolises.     

Spinach leaf dihydrodipicolinate synthase: Partial purification and characterization

The first enzyme unique to lysine biosynthesis in higher plants, dihydrodipicolinate synthase, has been partially purified from spinach leaves, using ion exchange chromatography, hydrophobic interaction chromatography and gel filtration. The spinach enzyme is moderately stable to short-term exposure to heat, in contrast to the pea leaf enzyme, but is unstable on storage even at ?20°. Thiol reagents interfere with the calorimetric assay used, and so cannot be routinely used to stabilize the enzyme, which has an active sulphydryl group. The MW of the enzyme is 115000 (gel filtration). Lysine is a potent inhibitor with an I_(0.5) of 2OμM, whilst the lysine analogue S-β-aminoethylcysteinc has an I_(0.5) of 400 μM. The Kt´_m for aspartic-β-semialdehyde was determined to be 1.4mM, but this compound demonstrated marked substrate inhibition at concentrations above 7 mM, increasing the apparent S_(0.5)for the second substrate, pyruvate.     

δ-Aminolaevulinate biosynthesis in the cyanobacterium Synechococcus 6301

The cyanobacterium (blue-green alga) Synechococcus 6301 incorporated a large amount of isotope from [1-¹⁴C] and [2-¹⁴C]acetate into phaeophorbide a obtained from chlorophyll a and into glutamatein cell protein; very little radioactivity was present in aspartate in cell protein. This distribution of isotope indicates that aspartate and the tetrapyrrole of chlorophyll a are not derived from a common C₄, precursor. The ratios of the specific radioactivities of phaeophorbide a to glutamate for organisms grown in the presence of 1-¹⁴C] and [2-⁴C ] acetate were 2.5:1 and 10:1 respectively. These are close to the theoretical values for the C₅, route to δ-aminolaevulinate which indicates that this is the only pathway to the tetrapyrrole precursor in Synechococcus 6301.