Metabolism of sulfur-containing amino acids by pregnant merino ewes

The availability and utilization of cystine and methionine were measured in single-bearing Merino ewes on three occasions, approximately 90, 110 and 130 days after mating, and the effects on these traits of sulfur amino acids (SAA) infused into the abomasum were also measured. Two levels of SAA were infused containing 0.5 or 1.0 g day-1 organic sulfur with DL-methionine contributing two-thirds and L-cystine one-third of the supplementary sulfur. The quantity of the diet offered was increased at each occasion so as to maintain maternal liveweight. The rates of irreversible loss of both cystine and methionine from plasma increased as pregnancy advanced, but the ratios between the rates of irreversible loss and intake of digestible organic matter (DOMI) did not vary with stage of pregnancy. The average daily rates of irreversible loss of cystine and methionine by the ewes consuming the diet alone were 13.6 and 119 mmol kg-1 DOMI respectively. The average rates of irreversible loss of methionine (Im, mmol h-1) and of cystine (Ic, mmol h-1) were both linearly (P less than 0.05) related to the rate of infusion of organic sulfur into the abomasum (s, g day-1): Im = 2.44 (+/- 0.33) s + 1.28 (+/- 0.13); and Ic = 0.16 (+/- 0.02) s + 0.30 (+/- 0.01). Five per cent of the rate of irreversible loss of cystine arose from trans-sulfuration of methionine by ewes consuming the ration only, but greater percentages (14 and 22%) were observed when the ration was supplemented with SAA (P less than 0.05). These transfer quotients were not influenced by stage of pregnancy. The stage of pregnancy did not influence the concentration of cystine or methionine in the plasma, but the abomasal infusions of SAA significantly increased the concentration of both SAA. The ewes consuming the basal diet were in positive balance for both nitrogen and sulfur. The retention of nitrogen did not vary with stage of pregnancy (average (s.e.), 5.8 (0.9) g day-1), but that of sulfur increased from 0.6 to 1.0 and 1.3 g day-1 in periods 1, 2 and 3, respectively (P less than 0.05). The retentions of nitrogen (N, g day-1) and of sulfur (S, g day-1) were linearly and significantly related to the rate of infusion of organic sulfur into the abomasum (s, g day-1): N = 2.7 (+/- 0.7)s + 4.4 (+/- 0.3); and S = 0.49 (+/- 0.03)s + 0.72 (+/- 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)     

A membrane-bound diacylglycerol kinase that selectively phosphorylates arachidonoyl-diacylglycerol. Distinction from cytosolic diacylglycerol kinase and comparison with the membrane-bound enzyme from Escherichia coli

The membrane-bound diacylglycerol kinase from Swiss 3T3 cells (M-DG kinase) was characterized with a mixed micellar assay system, and compared with the cytosolic diacylglycerol kinase from 3T3 cells and with the membrane-bound diacylglycerol kinase from Escherichia coli. M-DG kinase selectively phosphorylated arachidonoyl-diacylglycerols, at a rate 2- to 8-fold higher than that for other naturally occurring long-chain diacylglycerols. In contrast, the cytosolic 3T3 enzyme exhibited little or no selectivity among long-chain diacylglycerols but had higher activity with more soluble substrates such as 1,2-didecanoylglycerol. Comparison of the properties of M-DG kinase with those of the bacterial membrane-bound enzyme revealed that selectivity for arachidonoyl-diacylglycerol was unique to the mammalian enzyme. All three kinases were activated by phosphatidylserine, but activation did not alter the arachidonoyl selectivity of M-DG kinase. Phosphatidylserine activated M-DG kinase by increasing Vm and decreasing the apparent Km for diacylglycerol. High concentrations of diacylglycerol reduced the Ka for phosphatidylserine, but did not abolish the phosphatidylserine requirement for maximum activity. Examination of the thermal lability of M-DG kinase revealed that this enzyme was rapidly and selectively inactivated by preincubation with its preferred substrate. This novel effect may have obscured previous attempts to discern substrate selectivity. Taken together, the results provide evidence that M-DG kinase is an arachidonoyl-diacylglycerol kinase that may participate in the formation of arachidonoyl-enriched species of phosphatidylinositol.     

Botulinum neurotoxin type B. Its purification, radioiodination and interaction with rat-brain synaptosomal membranes

Neurotoxin from Clostridium botulinum type B was purified to homogeneity by by affinity and ion-exchange chromatography; specific neurotoxicity of this protein (Mr of approximately equal to 155 000) following trypsinisation attained a level of 2 X 10(8) mouse LD50 units/mg protein. 125I-iodination of the toxin to high specific radioactivities (19-63 TBq/mmol) yielded typically greater than 65% of its original toxicity; dodecyl sulphate gel electrophoresis under reducing conditions, after trypsinisation, showed that the larger polypeptide (Mr of approximately equal to 101 000) was labelled preferentially. Saturable binding of the 125I-labelled neurotoxin to rat cerebrocortical synaptosomes was observed and Scatchard analysis showed a low content of acceptors with high affinity (Kd = 0.3-0.5 nM;Bmax approximately equal to 30-60 fmol/mg protein, together with a much larger population of weak-affinity sites. No significant differences in binding affinity were seen in competition experiments using native or fully activated (trypsinized) neurotoxin, indicating that chain cleavage is not essential for acceptor-toxin interaction. Type A botulinum neurotoxin showed a limited capacity to inhibit the synaptosomal binding of labelled type B toxin, even at high concentrations (1 muM), and other neurotoxins were without effect, emphasising the acceptor selectivity. Near-complete loss of specific toxin binding was produced by preincubation of synaptosomes with neuraminidase whereas inhibition of the low-affinity sites with wheat-germ agglutinin was less pronounced; such inactivation was prevented by inclusion of selective inhibitors (2,3-dehydro-2-deoxy-N-acetylneuraminic acid and N-acetylglucosamine, respectively). These observations implicate N-acetylneuraminic acid and, possibly, other sugar moieties as constituents of the toxin acceptors. Trypsinisation of synaptosomes gave incomplete inhibition of binding when assayed with 1 nM or 10 nM 125I-iodinated toxin. Detailed analysis of the actions of neuraminidase, trypsin and heat treatment on the concentration dependence of toxin binding suggest the existence of at least two distinguishable populations of sites that contain N-acetylneuraminic acid, with a protein component being associated with the acceptors of lower affinity. These findings are discussed in relation to those previously reported for type A neurotoxin and to the possible physiological significance of such membrane acceptors.     

Recognition of vesicular lipoproteins by the apolipoprotein B,E receptor of cultured fibroblasts

Vesicular lipoproteins (e.g., lipoprotein-X) are found in plasma in cholestasis or following infusion of Intralipid or phospholipid. To investigate the metabolism of vesicular lipoproteins, we isolated them from the plasma of subjects with cholestasis or following chronic or single Intralipid infusion. Cholestasis and chronic Intralipid therapy were found to be associated with elevated plasma concentrations of apoE, as determined by radioimmunoassay. Vesicular lipoproteins purified from each of the three types of plasma contained apoE, as well as other proteins. In cholestasis, in which levels of apoE were up to five times normal, a major portion of the plasma apoE was on vesicular lipoproteins. Normalized for apoE content, all preparations of vesicular lipoproteins displaced 125I-labeled LDL from apoB,E receptors of cultured fibroblasts identically. This displacement was inhibited by monoclonal antibodies that block receptor binding of apoE. Vesicular lipoproteins containing 125I-labeled apoE were internalized and degraded by fibroblasts. Different preparations caused small losses or gains of cellular cholesterol, with appropriate stimulation or suppression of apoB,E receptors. Thus, vesicular lipoproteins contain apoE, and apoE mediates their interaction with the apoB,E receptor. Our results suggest that the catabolism of cholesterol-rich vesicular lipoproteins, formed during cholestasis or following infusions of Intralipid or phospholipid, may be receptor-mediated.     

Dimethylnitrosamine metabolism: II. In vitro activation of dimethylnitrosamine by hepatic and renal tissues from crosses among BALB/c, DBA and C57BL mice

Crosses among BALB/c, C57BL and DBA mice were performed to investigate the genetic mechanisms involved in metabolism of DMN by renal and hepatic tissues. Liver S-9 fractions from parental strain DBA had the greatest potential to activate DMN and liver fractions from parental strain BALB/c had the lowest. No age or sex-related differences were observed within strain. Crossing of either C57BL or DBA to BALB/c mice resulted in F1 hybrids with liver microsomal enzymes that gave results similar to the BALB/c parental strain. There were no sex or age differences within crossbred strains in the potential of liver to activate DMN. In contrast male DBA and C57BL parental mice renal S-9 fractions did not differ significantly from each other but did differ significantly from male BALB/c renal fractions and from female and immature animals of all strains. Crossing of either DBA or C57BL mice with BALB/c mice resulted in male F1 hybrids whose renal S-9 fractions did not differ significantly from males of the parental BALB/c strain. In all instances, male renal S-9 fractions had a significantly greater potential to activate DMN than female or immature animals. F1 DBA X C57BL hybrids had renal S-9 fractions that did not differ significantly from the parental strains. These data suggest that the gene(s) for low DMN metabolism of BALB/c mice are apparently dominant over the genes from both DBA and C57BL. The exact genetic or physiological mechanism needs further elucidation.     

THE OCCURRENCE OF PHYTOSEIULUS PERSIMILIS ATHIAS-HENRIOT (ACARINA:PHYTOSEIIDAE) IN AN ORCHARD IN VICTORIA

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High numbers of the predatory mite, Phytoseiulus persimilis , were found on apple and nectarine trees in a commercial orchard at Werribee, Victoria in February 1981. In the following season, again it was not detected on trees or broad-leaved weeds in the orchard until late summer. Slide-dip tests on the Werribee population of P. persimilis and a population originating from strawberries in Sydney, New South Wales, showed that azinphos-methyl was equally toxic to the 2 strains and DDT was considerably less toxic to both.     

Partial trisomy 11p with interatrial septal aneurysm. Case report and literature review

A newborn female infant presented with hypotonia, joint hyperextensibility, cardiac murmur, macroglossia, and hepatosplenomegaly. Karyotype of the child revealed partial trisomy of chromosome 11p derived from a paternal balanced translocation. Echocardiogram obtained in the newborn period suggested interatrial aneurysm, which was confirmed on post-mortem examination. Interatrial septal aneurysm is a rare abnormality not previously described in partial trisomy 11p.     

Evidence from cDNA clones that the rat leukocyte-common antigen (T200) spans the lipid bilayer and contains a cytoplasmic domain of 80,000 Mr

The leukocyte-common antigen (L-CA or T200) includes a family of lymphoid and myeloid cell surface glycoproteins with apparent molecular weights from 180,000 to 240,000. We report a partial protein sequence for thymocyte L-CA containing 1073 amino acids predicted from cDNA clones isolated using an oligonucleotide probe. Only one segment (residues 347-368) is likely to cross the membrane, and peptide data suggest that sequences N-terminal to this are outside the cell, with residues 369-1073 inside. The cytoplasmic domain includes possible phosphorylation sites and an internal homology between residues 385-671 and 676-986. Analysis of B lymphocyte cDNA clones suggests that B cell and thymocyte mRNAs are identical in 3' sequences, but size differences in Northern blots suggest 5' sequences may differ.