Properties of Kaurene Synthetase from Marah macrocarpus Endosperm: Evidence for the Participation of Separate but Interacting Enzymes

Ent-kaurene is synthesized from geranylgeranyl pyrophosphate in a two step sequence catalyzed by kaurene synthetase; the first step (A activity) involves the conversion of geranylgeranyl pyrophosphate into the intermediate ent-trans labda-8(17), 13-dien-15-yl pyrophosphate (copalyl pyrophosphate) which is further cyclized to ent-kaurene in the second step (B activity). The resolution of enzyme fractions which catalyze each step independent of the other has been accomplished for the first time by means of QAE Sephadex A-50 chromatography and polyacrylamide gel electrophoresis of kaurene synthetase preparations from endosperm tissue of immature seed of Marah macrocarpus. Molecular weights for the A and B enzymes were each estimated as approximately 82,000 by means of gel filtration chromatography and sedimentation velocity determinations.     

TRACHELOMONAS HISPIDA VAR. CORONATA (EUGLENOPHYCEAE). I. ULTRASTRUCTURE OF CYTOSKELETAL AND FLAGELLAR SYSTEMS1,2

Trachelomonas hispida var. coronata Lemm. has a fibrous, mucilaginous, ovoid, mineralized envelope (lorica), the ornamentation and coloration of which are capricious in culture. Cells exhibit a radial distribution of most organelles: (i) A cortical endoplasmic reticulum, (ii) parietal chloroplasts, and (iii) a median vacuolar region surrounded by several Golgi bodies and diverse vesicles. Associated with the emergent flagellum is a “paraflagellar complex” that consists of dense globules, cross-striated ribbon-like structures, a paraflagellar body, and an array of parallel striated filaments. The stigma consists of a single layer of pigmented granules that partially surrounds the canal/reservoir transition zone where microtubular bands intersect. A microtubular cytoskeleton consists of pellicular microtubules, peri-canal microtubules, stigma-associated microtubules and para-reservoir microtubules. The thickenings on the posterior, concave margins of the pellicular strips suggest that this pellicle is of intermediate complexity between those of Euglena spirogyra (Ehrenb. and Trachelomonas volvocina (Ehrenb.).     

Activation of 2',5'-oligo(A) polymerase and protein kinase of interferon-treated HeLa cells by 2'-O-methylated poly (inosinic acid) . poly(cytidylic acid), Correlations with interferon-inducing activity

An oligonucleotide polymerase and a protein kinase which require double-stranded RNA (dsRNA) for activation are induced in HeLa cells by human fibroblast interferon. The polymerase synthesizes a series of oligonucleotides from ATP, whereas the kinase phosphorylates a polypeptide of Mr = 72,000 and the alpha subunit of initiation factor eIF-2. Partially or fully 2'-O-methylated derivatives of poly(inosinic acid) . poly(cytidylic acid) (rIn . rCn) were used to determine the structural requirements of dsRNA in the activation of these two enzymes. While fully methylated polymers failed to activate either enzyme, partially methylated polymers activated the enzymes in specific manners. The activation of the kinase by the rIn . rCn analogues was affected more severely by the level of methylation than was the activation of the polymerase. Moreover, fully methylated analogues blocked the activation of the kinase by rIn . rCn but not the activation of the polymerase. These observations are consistent with a biphasic model for enzyme activation similar to that proposed for interferon induction, which required the recognition of a relatively small region of rIn . rCn as the last step. Differences in the activation of the polymerase and kinase are explicable on the basis of the polymerase requirement for a smaller recognition region of the rIn . rCn duplex than the kinase. Dependence of polymerase activation on the level of methylation shows striking similarities with the interferon inducing activities of these analogues, suggesting a possible relationship between polymerase activation and interferon induction.     

Prehistoric cultivated cucurbits from the Viru Valley,Peru

A sample of 535 specimens of cucurbits were retrieved from archaeological deposits in the Viru Valley, Peru, from contexts dated between ca. 1800 B.C.– 1100 A.D. by Carbon-14 analysis and cultural associations. Cultivars ofCucurbita maxima Duch. and C.moschata (Duch.) Duch. ex Poir. are found to be restricted, respectively, to early and late chronological periods, with no overlap. Cultural and ecological factors are suggested to account for the observed temporal and spatial variations in species occurrence. Comparison of materials from other coastal valleys indicat es significant, but presently unexplainable, spatial and temporal differences in the distribution of these species. Supportive evidence for South America as an independent center of domestication for C.maxima tis offered.     

Minireview possible roles of dietary fats in carcinogenesis

Epidemiological data have implicated dietary fat as an important factor in the aetiology of various cancers in humans. This suggestion is supported by the results of experiments with animals which have shown that increased amounts of dietary fat, in particular polyunsaturated fat, increase the incidence of some spontaneous and induced tumours. The enhancement of carcinogenesis by dietary fats appears to be exerted at the promotional stage of carcinogenesis. Changes induced by dietary fats in several biological systems involved in carcinogenesis may well indicate the underlying mechanisms responsible for the results of these experiments. These include the effects of dietary fats on the metabolism of chemical carcinogens, the structure and function of membranes, immunocompetence, DNA repair potential and endocrine function.     

Recruitment in networks of pulmonary capillaries.

To improve our understanding of the pressure-flow characteristics of pulmonary capillaries, we analyzed by means of computer stimulation a theoretical model composed of 50 interconnected nonlinear elements. Each element required a critical pressure across it before flow occurred and there was a subsequent linear pressure-flow region whose slope, or resistance, could be related to the transmural pressure of the element ("distensibility"). The critical pressures and resistances of each element of the network were randomly chosen from distributions. We found that recruitment (i.e., onset of flow) occurred over a large range of network upstream or "arterial" pressures, and that relatively high arterial pressures were required before all elements had no distensibility. Intermittent and reverse flow were commonly seen in some elements as the arterial pressure was raised in steps. These flow reversals were particularly common when the critical pressures and resistances of the elements were inversely related. The critical pressures required for such behavior in the capillary segments of the pulmonary microcirculation were calculated to be extremely small, of the order of 0.02 cmH2O. Pressures of this magnitude might result from sticking of red cells to capillary walls or to each other. The properties of such a network may explain the patchiness of flow in the pulmonary microcirculation and the large range of arterial pressures over which recruitment is observed to occur.