Adaptive synthesis of fatty acid synthetase and acetyl-CoA carboxylase by isolated rat liver cells.

Hepatocytes were isolated at specified times from livers of diabetic and insulin-treated diabetic rats during the course of a 48-h refeeding of a fat-free diet to previously fasted rats. The rates of synthesis of fatty acid synthetase and acetyl-CoA carboxylase in the isolated cells were determined as a function of time of refeeding by a 2-h incubation with l-[U-¹⁴C]leucine. Immunochemical methods were employed to determine the amount of radioactivity in the fatty acid synthetase and acetyl-CoA carboxylase proteins. The amount of radioactivity in the fatty acid synthetase synthesized by the isolated cells was also determined following enzyme purification of the enzyme to homogeneity. Enzyme activities of the fatty acid synthetase and acetyl-CoA carboxylase in the cells were measured by standard procedures. The results show that isolated liver cells obtained from insulintreated diabetic rats retain the capacity to synthesize fatty acid synthetase and acetyl-CoA carboxylase. The rate of synthesis of the fatty acid synthetase in the isolated cells was similar to the rate found in normal refed animals in in vivo experiments [Craig et al. (1972) Arch. Biochem. Biophys. 152, 619–630; Lakshmanan et al. (1972) Proc. Nat. Acad. Sci. USA69, 3516–3519]. In addition the relative rate of synthesis of fatty acid synthetase was stimulated greater than 20-fold in the diabetic animals treated with insulin. Immunochemical assays, when compared with enzyme activities, indicated the presence of an immunologically reactive, but enzymatically inactive, form or “apoenzyme” for both the fatty acid synthetase and acetyl-CoA carboxylase. The synthesis of these immunoreactive and enzymatically inactive species of protein, as well as the synthesis of the “holoenzyme” forms of both enzymes, requires insulin.     

Metabolism and biological potency of 5,6-monoepoxy-β-carotene and 5,6:5′,6′-diepoxy-β-carotene

1. 5,6-Monoepoxy-beta-carotene and 5,6:5',6'-diepoxy-beta-carotene were partially converted into the furanoid forms during passage through the rat stomach. 2. The monoepoxide was converted into vitamin A in the small intestine and showed a biological potency 21% of that of beta-carotene. Neither beta-carotene nor 5,6-monoepoxyvitamin A was formed. 3. Intraperitoneal administration of the monoepoxide led to the accumulation of the unchanged compound in the liver and other tissues. 4. The diepoxide gave no beta-carotene or vitamin A or 5,6-monoepoxyvitamin A when given orally and showed no biological potency. 5. The significance of these results with special reference to the mechanism of formation of vitamin A from beta-carotene is discussed.     

Investigation of intermolecular interactions and stability of verubecestat in the active site of BACE1: Development of first model from QM/MM-based charge density and MD analysis

Alzheimer disease (AD) is a cruel neurodegenerative disorder caused by the deposition of amyloid β (Aβ) peptide inside the brain. The β-secretase (beta amyloid precursor protein (APP) cleaving enzyme 1, BACE1) is one of the enzymes involved in the cleavage of APP that leads to the Aβ formation and it is the primary target for the treatment of AD. Recent report outlines that verubecestat molecule strongly inhibits BACE1; however, its structure, binding mechanism and the stability in the active site of BACE1 are not yet known. The present study aims to determine the structure, binding affinity and the stability of verubecestat molecule in the active site of BACE1 from the molecular docking, quantum mechanics/molecular mechanics (QM/MM)-based charge density analysis and molecular dynamics simulation. Verubecestat molecule was docked at BACE1; it shows high binding affinity towards BACE1. Further, the conformational geometry and the intermolecular interactions of verubecestat in the active site of BACE1 were determined. The molecule forms strong interaction with the neighboring amino acids in the active site of BACE1. The onsite QM/MM-based charge density analysis reveals the nature of charge density distribution and the topological properties of intermolecular interactions of verubecestat molecule in the active site of BACE1. The calculated electrostatic potential (ESP) of verubecestat in the active site of BACE1 displays high negative and positive ESP regions of the molecule. This onsite QM/MM analysis is more relevant to the physiological situation. The molecular dynamics simulation has been performed, which confirms the high stability and compactness of verubecestat in the active site of BACE1. The MM-generalized Born surface area and MM-Poisson Boltzmann surface area free energy calculations of verubecestat–BACE1 also confirm the high binding affinity of verubecestat.

Communicated by Ramaswamy H. Sarma     

Changes in carbohydrate metabolism by triazole growth regulators in cassava (Manihot esculenta Crantz); effects on tuber production and quality

We have evaluated the ability of two triazole growth regulators, viz. triadimefon (TDM) and hexaconazole (HEX), in the enhancement of tuber production and quality in cassava (Manihot esculenta Crantz) through their effects on carbohydrate metabolism. One litre of 20 mg(-1) TDM and 15 mg(-1) HEX solution per plant were used for the treatments and groundwater was given to control plants. Triazole treatments reduced plant height and leaf area, but increased fresh and dry weights. Plants treated with TDM showed an increased net assimilation rate, which is followed by HEX and control plants. Triazole compounds increased the relative growth rate of cassava after 200 DAP, i.e. in the phase of tuber enlargement. Triazole compounds increased the starch and other carbohydrate contents and carbohydrate metabolising enzyme activities. From the results of this study, it can be concluded that these triazoles can significantly enhance the tuber production and quality by affecting the starch metabolism, apart from their fungicidal properties.     

Genetic fidelity of long-term micropropagated shoot cultures of vanilla (Vanilla planifolia Andrews) as assessed by molecular markers

Occurrence of genetic variants during micropropagation is occasionally encountered when the cultures are maintained in vitro for long period. Therefore, the micropropagated multiple shoots of Vanilla planifolia Andrews developed from axillary bud explants established 10 years ago were used to determine somaclonal variation using random amplified polymorphic DNA (RAPD) and intersimple sequence repeats markers (ISSR). One thousand micro-plants were established in soil of which 95 plantlets (consisting of four phenotypes) along with the mother plant were subjected to genetic analyses using RAPD and ISSR markers. Out of the 45 RAPD and 20 ISSR primers screened, 30 RAPD and 7 ISSR primers showed 317 clear, distinct and reproducible band classes resulting in a total of 30 115 bands. However, no difference was observed in banding patterns of any of the samples for a particular primer, indicating the absence of variation among the micropropagated plants. Our results allow us to conclude that the micropropagation protocol that we have used for in vitro proliferation of vanilla plantlets for the last 10 years might be applicable for the production of clonal plants over a considerable period of time.