Optimisation of conditions for the degradation of mimosine in Leucaena leucocephala leaf

A study was made of the rate of degradation of mimosine to 3-hydroxy-4(1H)-pyridone in harvested leucaena leaf under various conditions. Optimum rates of degradation of an aqueous leucaena slurry were at pH 8.0 and 45°C with virtual total loss of mimosine in 10 min. Heating the intact leaf also reduced the mimosine content with the maximum rate of degradation at 70°C. The results have implications for reducing the toxicity of leucaena used for stock feed.     

Intravenous RMP-7 increases delivery of ganciclovir into rat brain tumors and enhances the effects of herpes simplex virus thymidine kinase gene therapy

Herpes simplex virus thymidine kinase (HSV-tk) gene therapy for brain tumors depends on ganciclovir (GCV) and its transport across the blood-brain tumor barrier (BBTB). We examined whether RMP-7, the bradykinin analog and potent BBTB permeabilizer, could enhance the efficacy of GCV treatment of brain tumors by increasing the BBTB delivery of GCV. In vitro, a significant bystander cytocidal effect of GCV was shown in mixed HSV-tk-transduced (HSV-tk+) and control vector-transduced (HSV-tk-) C6 glioma cultures. A dose-dependent cytotoxic effect of GCV on untransformed C6 cells was also shown. In vivo, rats with 100% HSV-tk+ or 100% HSV-tk- intracerebral C6 gliomas were treated for 7 days with intravenous infusions of GCV alone or with GCV and RMP-7 (2.5 microg/kg/day). The growth of HSV-tk+ and HSV-tk- gliomas decreased with increasing doses of GCV. A high dosage (100 mg of GCV/kg/day) eradicated all HSV-tk- and HSV-tk+ tumors. An intermediate dosage (5 mg of GCV/kg/day) reduced the growth of HSV-tk- gliomas by 42% if given alone, and by 88% in combination with RMP-7. A low dosage (0.5 mg of GCV/kg/day) in combination with RMP-7 enhanced the regression of HSV-tk+ gliomas by 87% compared with GCV alone. Low-dose GCV was ineffective in HSV-tk- tumors. RMP-7 increased [3H] GCV tumoral uptake by 2.6- and 1.7-fold in the tumor center and periphery, respectively. We conclude that RMP-7 could be an important adjunctive treatment for suicide gene therapy of brain tumors, while an RMP-7/GCV combination may also have a significant antitumor effect in untransfected gliomas.     

An isotopic method for determining chemically reactive lysine based on succinylation

A method is described for the routine succinylation of proteins using [¹⁴C]succinic anhydride as a means of measuring free ?-amino groups. Maximal succinylation was achieved using 6M guanidine hydrochloride as protein solvent and an 80-fold molar excess of succinic anhydride relative to total lysine residues. Treatment with hydroxylamine (pH 13, 25°C, 5 min) removed unwanted O-succinyl esters. Succinylated protein was precipitated with trichloroacetic acid, residual label washed out with ethanol and the extent of labelling measured in a scintillation counter. The method gave close to theoretical values (n.s., P >0.05) for lysyl residues in egg white lysozyme, bovine haemoglobin, ovalbumin and bovine serum albumin but gave a low value with β-lactoglobulin and an overestimate with insulin attributable to the relatively high contribution of α- relative to ?-amino groups in this low molecular weight protein. The method gave good results for 12 soya protein samples and was shown to be very sensitive to ‘isopeptide-type’ heat damage in these samples. The results correlated well (r = 0.91) with those obtained by the well established dye-bound lysine difference procedure whereas, as could be expected, both these methods correlated poorly with total lysine determinations (r=0.69 for succinic anhydride and r=0.77 for the dye-binding method). The proposed method shows promise as a rapid procedure for the estimation of available lysine, but further studies are necessary to test its ability to measure nutritionally available lysine in all categories of heat damage.     

Effect of diet on the fatty acid and molecular species composition of dog retina phospholipids

Dogs were born to mothers fed commercial diets low or enriched in n-3 fatty acids and raised on those diets until they were about 50 d old. Retinas were removed, lipids were extracted, and total phospholipids were analyzed for fatty acid and molecular species composition. Animals from the low n-3 group had significantly lower retinal levels of 22:6n-3 and higher levels of n-6 fatty acids, especially 20:4n-6 and 22:5n-6. There was no difference in the retinal levels of 18:2n-6, and only small differences were found in saturated and monounsaturated fatty acids. The most dramatic differences in molecular species occurred in 22:6n-3-22:6n-3 (4.7 vs. 0.8%) and 18:0-22:6n-3 (27.6 vs. 14.4%); total molecular species containing 22:6n-3 were significantly lower in the low n-3 group (45.5 vs. 24.0%). Molecular species containing 20:4n-6 and 22:5n-6 were greater in the low n-3 animals (13.0 vs. 25.7%), as were molecular species containing only saturated and monounsaturated fatty acids (40.8 vs. 35.4%). These results show that modest differences in the amount of n-3 fatty acids in the diets of dogs can have profound effects on the fatty acid and molecular species composition of their retinas.     

Effect of arachis oil on the conservation of heavily wilted herbage ensiled in plastic containers. II. Fate of the arachis oil and its effect on the rumen volatile fatty acids of sheep

Arachis oil was added to heavily wilted ryegrass at a mean level of 4 · 16 % of the total ensiled dry matter. Gas-liquid chromatography of the lipid extract was used to investigate possible chemical changes in the ensiled oil. The data obtained suggest that little degradation of the acids occurred. The percentage of linolenic acid increased and this was accompanied by a decrease in the percentage of linoleic acid and oleic acid. The presence of the oil decreased the volatile fatty acid content of the silage. There were no significant differences in the pH or the proportion of volatile fatty acids present in the rumen liquor of sheep fed the oil-treated silage compared with those in the rumen liquor of sheep fed control silage.     

Effect of staphylococcal alpha-toxin pancreatitis on glucose tolerance in the dog

Acute pancreatitis was experimentally produced in dogs to study the effect of the disease on glucose tolerance. The k value (glucose disappearance coefficient measured in percentage decrease of glucose/min) calculated from the high-dose intravenous glucose-tolerance test was used to evaluate the glucose tolerance of each dog. Thirty dogs were allotted to 3 groups of 10 dogs each as follows: group I--nonsurgical control dogs; group II--surgical control dogs; and group III--pancreatitis-affected dogs. To increase their susceptibility to diabetes, 50% partial pancreatectomies and ductal catheterizations were performed on group II and III dogs. Saline solution was infused into the ductal systems of group II dogs, and staphylococcal alphatoxin was infused into the ductal systems of group III dogs to produce pancreatitis. The results indicated that (1) high-dose intravenous glucose-tolerance test was an effective tool for determining decreased glucose tolerance in dogs; (2) glucose tolerance of group III dogs was markedly decreased compared with that of group I and II dogs; (3) staphylococcal alpha-toxin produced signs of moderately severe pancreatitis; and (4) 50% partial pancreatectomy and saline solution infusion produced clinical and clinicopathologic signs of mild pancreatitis. To determine if a simplified k value (calculated using 2 or 3 blood samples) could closely approximate the standard k value (calculated using 6 blood samples), simplified k values were derived from the 5- and 60-minute blood sample values. These values closely approximated the standard k values, indicating the simplified value may be used in the clinical situation. The standard k value, however, is preferred for investigative work.     

MOSFET's in the 0°K approximation: Static characteristics of MOSFET's in the 0°K approximation

The static electrical characteristics below current saturation of MOSFET's with degenerate source and drain regions are calculated for operation at 0°K. The expression for current takes the same form as at room temperature although the flat-band voltage and the voltage across the depletion region at threshold are altered slightly. Potential hills occur in the channel if the gate does not overlap source and drain or if the oxide thickness is increased in the overlap regions. Although these barriers do not affect operation appreciably at room temperature, at 0°K a finite drain voltage (source-drain threshold voltage) is required to initiate conduction. This threshold voltage is included in the theory and the theory is compared with experimental results on p-channel enhancement mode MOSFET's at 4·2°K using hole mobility in the channel as a matching parameter. The channel hole mobility (assumed constant along the channel) is found to be relatively independent of gate voltage but to increase with increasing (negative) drain voltage. Values ranging between 500 and 1000 cm²/V-sec are deduced for drain voltages ranging from ?1·2 V to ?7 V. This compares to channel hole mobility values of 200–300 cm²/V-sec at room temperature. It is found that the channel width is on the order of 30–50 Å—appreciably less than that at room temperature.