Increase in activity and biosynthesis of phospholipase A of Entamoeba histolytica by cholesterol passage

Phospholipase A (EC 3.1.1.4) activity was detected in trophozoites and cell-free culture medium of Entamoeba histolytica NIH-200. The enzyme from both the sources gave two pH optima at 4.2 and 9.0 and was stimulated by addition of CaCl₂. Cholesterol passage of the amoeba increased the enzyme activity and trophozoite-multiplication. The enzyme was purified by submitting the trophozoites to freezing and thawing, treatment with triton X-100, heat denaturation, and chromatography on Sephadex G-100. The purified enzyme resolved on sodium dodecyl sulphate gel electrophoresis into two protein bands, one exhibiting optimal phospholipase A activity at pH 4.2 and the other at pH 9.0. Incorporation of ¹⁴C ammo acids into the proteins at various stages of enzyme purification suggests that cholesterol passage increased the synthesis and activity of phospholipase A in the trophozoites.     

Hydrolysis of storage proteins in barley endosperms : analysis of soluble products

Soluble products, released by the hydrolysis of hordeins into the media of barley (Hordeum vulgare cv. Perth) half-seeds were analyzed. Large polypeptide fragments (methanol-insoluble) were identified using the Western immunoblot technique with the antibodies prepared against B and C polypeptides of hordein. A number of hordein IgG-reacting bands were noted in the samples from dry kernels. In samples incubated in the absence of gibberellic acid, polypeptide fragments in the size range of 25 to 30 kilodaltons appeared within 24 hours, and those in the size range of 40 kilodaltons became more prominent. In samples incubated in the presence of gibberellic acid, polypeptide fragments in the size range of 45 to 67 kilodaltons were less apparent and those in the size range of less than 15 kilodaltons were more pronounced. The hordein-related polypeptide fragments were present in low amounts after 72 hours in the presence of gibberellic acid. Methanol-soluble peptides were fractionated, on the basis of size, into two broad peaks. In the absence of gibberellic acid, there was no significant change in their profile over a 72 hour incubation period. In the presence of this growth substance, however, there was a decrease in the proportion of large size peptides (50-70 amino acid residues in length), and an increase in the levels of small peptides (15-35 amino acid residues in length) and amino acids. Our interpretation of the results is that the release of the initial large polypeptide fragments from hordein proteins is mediated by a protease(s) whose appearance is not dependent on the exogenously added gibberellic acid. Further hydrolysis is, however, mediated by proteases induced in the presence of this growth substance.     

Alkaloids of Litsaea laeta and L. salicifolia

The structure for laetine (2-hydroxy-1-methyl 10,11-methylenedioxy noraporphine), a new alkaloid from the bark of Litsaea laeta has been established. N,O-Dimethylharnovine and glaucine were also isolated from the same source. C-2 hydroxy aporphines are characteristic of L. laeta. Two known alkaloids, dicentrinone and nordicentrine, have also been isolated from the leaves of L. salicifolia.     

Structure of asclepin and some observations on the NMR spectra of Calotropis glycosides

Asclepin has been shown to be 3′-O-acetylcalotropin using various chemical and physical methods. The NMR data of all the Calotropis glycosides have been analysed in conjunction with that of asclepin, certain anomalies have been pointed out and revised structures have been proposed for the acetylated glycosides.     

Steroids and related products. 38. 11-Aza steroids. 3. The synthesis of 11-aza 9 -steroids. I

The synthesis of 3,20-dioxygenated 11-azapregnanes, with a “normal” (a) configuration.in position 9, is described. The saturation of the 8,9-double bond of previously described unsaturated precursors can be effected not only by reduction of 9,11-iminium salts, but also catalytically, under pressure, in the presence of perchloric acid, It is shown that the 7-position of 8,9-unsaturated 11-aza steroids can be functionalized with the chromic acid-pyridine complex, the double bond of the resulting 7-ketone being prone to Birch reduction. Other, direct, pathways from saturated 11-nor 9,12-seco steroids to saturated 11-aza 9α-steroids have been explored. The crucial difficulty inherent in this approach stems from the fact that in displacement reactions involving an axial 9α-substituent, elimination competes successfully with substitution.     

Polyamine Metabolism in Ripening Tomato Fruit : II. Polyamine Metabolism and Synthesis in Relation to Enhanced Putrescine Content and Storage Life of a/c Tomato Fruit

The fruit of the Alcobaca landrace of tomato (Lycopersicon esculentum Mill.) have prolonged keeping qualities (determined by the allele a/c) and contain three times as much putrescine as the standard Rutgers variety (A/c) at the ripe stage (ARG Dibble, PJ Davies, MA Mutschler [1988] Plant Physiol 86: 338-340). Polyamine metabolism and biosynthesis were compared in fruit from Rutgers and Rutgers-a/c—a near isogenic line possessing the allele a/c, at four different stages of ripening. The levels of soluble polyamine conjugates as well as wall bound polyamines in the pericarp tissue and jelly were very low or nondetectable in both genotypes. The increase in putrescine content in a/c pericarp is not related to normal ripening as it occurred with time and whether or not the fruit ripened. Pericarp discs of both normal and a/c fruit showed a decrease in the metabolism of [1,4-¹⁴C]putrescine and [terminal labeled-³H]spermidine with ripening, but there were no significant differences between the two genotypes. The activity of ornithine decarboxylase was similar in the fruit pericarp of the two lines. Arginine decarboxylase activity decreased during ripening in Rutgers but decreased and rose again in Rutgers-a/c fruit, and as a result it was significantly higher in a/c fruit than in the normal fruit at the ripe stage. The elevated putrescine levels in a/c fruit appear, therefore, to be due to an increase in the activity of arginine decarboxylase.