Distribution of podolactone-type plant growth inhibitors in the coniferae

Plant growth inhibitors of the podolactone-type have been detected by bioassay in ten further species of Podocarpus. The most active extracts in P. elatus were from root tips, root cortex and very young leaves. Fifty-seven other conifers were examined for this type of activity. It is present in Cephalotaxus harringtonia where it is probably due to the presence of harringtonolide, which, like momilactone B from rice husks, shows podolactone-type inhibition of the growth of etiolated dwarf pea hooks.     

Effects of canavanine on IAA- and fusicoccin-stimulated cell enlargement, proton extrusion and potassium uptake in maize coleoptiles

In maize coleoptiles (Zea mays F₁ XL 640A, cv. Dekalb) canavanine and cycloheximide strongly and simultaneously inhibit cell elongation, H⁺ extrusion and K⁺ uptake, induced by IAA. They inhibit also, although to a much lesser degree, the same phenomena induced by fusicoccin. Cycloheximide severely depresses the incorporation of leucine into proteins, while canavanine leaves leucine incorporation almost unchanged. The data confirm that elongation, H⁺ extrusion and K⁺ uptake can be regarded as correlated processes; they also support the view that normal protein synthesis is essential for IAA-induced growth, while this requirement is only partial in growth stimulated by fusicoccin.     

Isolation and characterization of trypsin inhibitors from cowpea (Vigna unguiculata)

The trypsin inhibitor fraction from cowpea (Vigna unguiculata) has been purified and characterized. Although the total trypsin inhibitor as purified by affinity chromatography on immobilised trypsin was shown to be heterogeneous by gel electrophoresis and isoelectric focusing as well as by function, it was relatively homogeneous in MW (ca 17 000) on gel filtration. The total trypsin inhibitor was divided into inhibitors active against trypsin only and active against trypsin and chymotrypsin by affinity chromatography on immobilised chymotrypsin. The ‘trypsin-only’ inhibitor was the major component of the total trypsin inhibitor. It was shown by isoelectric focusing and gel electrophoresis to contain several isoinhibitors. Determination of the combining weight of this inhibitor and investigation of the complexes formed with trypsin by gel filtration indicated the presence of two protease binding sites per inhibitor molecule. The chymotrypsin/trypsin inhibitor was also shown to be composed of several isoinhibitors. On the basis of gel electrophoresis and gel filtration in dissociating and non-dissociating media both inhibitors were considered to be dimeric molecules with the subunits linked by disulphide bonds; this implies that the ‘trypsin-only’ inhibitor has one binding site per subunit.     

Studies on trypsin inhibitors in the tubers of cocoyam (Xanthosoma sagittifolium)

Trypsin (EC 3.4.21.4) inhibitors have been isolated and purified by gelfiltration and ion exchange chromatography from the tubers of cocoyam (Xanthosoma sagittifolium). Three isoinhibitors were obtained in an electrophoretically homogeneous state. Their molecular weights estimated by molecular sieve chromatography were found to be 19 950, 17 780 and 23 390, respectively. They showed varied trypsin inhibitory activity which was lost on boiling for 40 min. They were found to have a maximum activity at pH 7.5–8.0.     

Studies on the lipid metabolism of the metacercariae of Clinostomum complanatum (Trematoda: Digenea)

Metacercariae of Clinostomum complanatum possess considerable amounts of lipids. Fractionation of the lipids shows triglycerides and phospholipids as the major components whereas cholesterol and free fatty acids are minor components. Furthermore phospholipid fractions by thin layer chromatography reveal lecithin and cephalin as the major polar lipids whereas lysolecithin and lysocephalin are present in small fractions. The specific activity of lipase (E.C. 3.1.1.3) is 150.8 μg free fatty acids liberated/mg protein/h. Epinephrine, testosterone, insulin, sodium fluoride and iodoacetate stimulated, but 2-propanol inhibited, the lipase activity.     

Schistosoma mansoni: thiol proteinase properties of adult worm "hemoglobinase".

This report presents evidence that the “hemoglobinase” from adult Schistosoma mansoni, first described by Timms and Bueding and later by Senft and his collaborators, belongs to the class of thiol proteinases. Proteolytic activity is stimulated by SH-containing compounds and inhibited by N-ethylmaleimide as well as other inhibitors of thiol proteinases. The enzyme can be partially purified by affinity chromatography using a Sepharose-linked organomercurial ligand. In addition to its activity on globin and hemoglobin, the enzyme can also be assayed with Azocoll, a general protease substrate, and by the activation of inactive trypsinogen to active trypsin. Extraction of the enzyme is enhanced by the addition of the nonionic detergent Triton X-100.     

Effect of ay-9944 on sterol biosynthesis in Chlorella sorokiniana

When Chlorella sorokiniana was grown in the presence of 4 ppm AY-9944 total sterol production was unaltered in comparison to control cultures. However, inhibition of sterol biosynthesis was shown by the accumulation of a number of sterols which were considered to be intermediates in sterol biosynthesis. The sterols which were found in treated cultures were identified as cyclolaudenol, 4α,14α-dimethyl-9β,19-cyclo-5α-ergost-25-en-3β-ol, 4α,14α-dimethyl -5α-ergosta-8,25-dien-3β-ol, 14α-methyl-9β,19-cyclo-5α-ergost-25-en-3β-ol, 24-methylpollinastanol, 14α-methyl-5α-ergost-8-en-3β-ol, 5α-ergost -8(14)-enol, 5α-ergost-8-enol, 5α-ergosta-8(14),22-dienol, 5α-ergosta-8,22-dienol, 5α-ergosta-8,14-dienol, and 5α-ergosta-7,22-dienol, in addition to the normally occurring sterols which are ergosterol, 5α-ergost-7-enol, and ergosta-5,7-dienol.The occurrence of these sterols in the treated culture indicates that AY-9944 is an effective inhibitor of the Δ⁸ → Δ⁷ isomerase and Δ¹⁴-reductase, and also inhibits introduction of the Δ²²-double bond. The occurrence of 14α-dimethyl-5α-ergosta-8,25-dien-3β-ol and 14α-methyl-9β,19-cyclo-5α-ergost -25-en-3β-ol is reported for the first time in living organisms. The presence of 25-methylene sterols suggests that they, and not 24-methylene derivatives, are intermediates in the biosynthesis of sterols in C. sorokiniana.     

Oncogenic KRAS G12C: Kinetic and redox characterization of covalent inhibition

The recent development of mutant-selective inhibitors for the oncogenic KRAS^G12C allele has generated considerable excitement. These inhibitors covalently engage the mutant C12 thiol located within the phosphoryl binding loop of RAS, locking the KRAS^G12C protein in an inactive state. While clinical trials of these inhibitors have been promising, mechanistic questions regarding the reactivity of this thiol remain. Here, we show by NMR and an independent biochemical assay that the pK_a of the C12 thiol is depressed (pK_a ∼7.6), consistent with susceptibility to chemical ligation. Using a validated fluorescent KRAS^Y137W variant amenable to stopped-flow spectroscopy, we characterized the kinetics of KRAS^G12C fluorescence changes upon addition of ARS-853 or AMG 510, noting that at low temperatures, ARS-853 addition elicited both a rapid first phase of fluorescence change (attributed to binding, K_d = 36.0 ± 0.7 μM) and a second, slower pH-dependent phase, taken to represent covalent ligation. Consistent with the lower pK_a of the C12 thiol, we found that reversible and irreversible oxidation of KRAS^G12C occurred readily both in vitro and in the cellular environment, preventing the covalent binding of ARS-853. Moreover, we found that oxidation of the KRAS^G12C Cys12 to a sulfinate altered RAS conformation and dynamics to be more similar to KRAS^G12D in comparison to the unmodified protein, as assessed by molecular dynamics simulations. Taken together, these findings provide insight for future KRAS^G12C drug discovery efforts, and identify the occurrence of G12C oxidation with currently unknown biological ramifications.