Defective brush-border expression of intrinsic factor-cobalamin receptor in canine inherited intestinal cobalamin malabsorption

Ligand binding activity of intrinsic factor-cobalamin receptor (IFCR) was determined in homogenates and isolated brush-border membranes (BBM) of ileum and kidney from dogs exhibiting simple autosomal recessive inheritance of selective cobalamin malabsorption (Fyfe, J. C., Giger, U., Hall, C. A., Jezyk, P. F., Klumpp, S. A., Levine, J. S., and Patterson, D. F. (1991) Pediatr. Res. 29, 24-31). IFCR activity of affected dog ileal homogenates was 3-4-fold higher than normal whereas IFCR activity in affected dog kidney homogenates was one-tenth of normal. The recovery of IFCR activity in the BBM of ileum and renal cortex of affected dogs was 30- and 20-fold less than normal, respectively. The dissociation constant (Kd) for intrinsic factor-cobalamin was similar in BBM of both tissues and was the same in affected and normal dogs. In the affected dog ileal BBM, activities of alkaline phosphatase and sucrase-isomaltase and vesicular transport of glucose and Na(+)-taurocholate were normal. Immunoblots showed no IFCR cross-reactive material in the ileal or renal BBM of affected dogs. IFCR purified by affinity chromatography from kidney of both normal and affected dogs had an Mr = 230,000. However, amino acid analysis revealed that the affected dog IFCR had more lysine than the normal, and protease cleavage of the purified IFCRs revealed different peptide maps. Asparagine-linked oligosaccharides of both proteins were sensitive to peptide N-glycosidase F cleavage, but only the affected dog IFCR was endoglycosidase H sensitive. These results suggest that cobalamin malabsorption in this canine family is caused by inefficient BBM expression of IFCR due to a mutation of IFCR and its retention in an early biosynthetic compartment.     

Transport characteristics of L-glutamate in human jejunal brush-border membrane vesicles

Previous work using human jejunal brush-border membrane vesicles has demonstrated the existence of a distinct transport system in man for acidic amino acids. This system is energized by an inwardly directed Na+ gradient and an outwardly directed K+ gradient. These studies further characterize the transport of L-glutamate in the human jejunal brush-border membrane vesicles. Efflux studies were performed by loading the brush-border membrane vesicles with radiolabeled L-glutamate and sodium chloride. Extravesicular K+ accelerated the efflux of L-glutamate when compared to extravesicular Na+ or choline, indicating that potassium serves to recycle the carrier. Unlabeled extravesicular L-glutamate (but not D-glutamate) also enhanced the efflux of radiolabeled L-glutamate demonstrating that there is a bidirectional similarity to the transport system. The effect of pH on the transport system was also investigated by varying the intravesicular and extravesicular pH from 5.5 to 9. A pH environment of 6.5 produced the highest initial uptake rates as well as the greatest overshoots for transport of L-glutamate into brush-border membrane vesicles. The imposition of an inwardly directed pH gradient (5.5 outside, 7.5 inside) accelerated both the influx and efflux of L-glutamate. These results demonstrate that the L-glutamate carrier system in human jejunum appears to have similar energizing characteristics in either direction across the brush-border membrane. In addition, the system operates at an optimal pH of 6.5 and protonation of the system may enhance its mobility.     

Periodicity of oviposition,feeding, and calling by mated femaleHeliothis virescens in a field cage

This paper describes behaviors exhibited by mated, 3-day-old female Heliothis virescensin the presence of flowering cotton infield cages in mid-July. Females exhibit discrete periods of egg deposition, calling, and feeding during scotophase. Females exhibit behaviors such as walking while wing fanning, wing buzzing, antennal movement, bending of abdomen, and dragging of the ovipositor on the substrate before egg deposition. These behaviors are interspersed with flight and calling. The number and duration of some behaviors differ when the female is ovipositing on cotton plants versus cage screen. Egglaying occurs in several major bouts through the scotophase with periods of inactivity or other activities interspersed. Most eggs are laid before 0300 h. Significant calling is observed after 0100 h and continues until about 0430 h. Although females exhibit some feeding near sunset, the major feeding activity is seen just prior to and after sunup.     

Crystal structure of cadaverine dihydrochloride monohydrate.

The structure of cadaverine dihydrochloride monohydrate has been determined by X-ray crystallography with the following features: NH3+ (CH2)5NH3+.2Cl-.H2O, formula weight 191.1, monoclinic, P2, a = 11.814(2)A, b = 4.517(2)A, c = 20.370(3)A, beta = 106.56 degrees (1): V = 1041.9(2)A3; lambda = 1.541A; mu = 53.41; T = 296 degrees; Z = 4, Dx = 1.218 g.cm-3, R = 0.101 for 1383 observed reflections. The crystal is highly pseudo-symmetric with 2 molecules of cadaverine, 4 chloride ions and 2 partially disordered water molecules present in the asymmetric unit. Though both the cadaverine molecules in the asymmetric unit have an all trans conformation, the carbon backbones are slightly bent. Between the concave surfaces of two bent cadaverine molecules exists water channels all along the short b axis. The water molecules present in the channels are partially disordered.     

The Distinctive Pattern of Photosystem 2 Activity,Photosynthetic Pigment Accumulation,and Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Content of Chloroplasts along the Axis of Primary Wheat Leaf Lamina

Wheat (Triticum aestivum L. cv. Sonalika) seedlings were grown in Hoagland solution. Primary leaves were harvested at 8, 12, and 15 d and cut into five equal segments. Contents of photosynthetic pigments and proteins, and photosystem 2 (PS2) activity increased from base to apex of these leaves. Chlorophyll (Chl) content was maximum at 12 d in all the leaf segments, but PS2 activity showed a gradual decline from 8 to 15 d in all leaf segments. In sharp contrast, the CO₂ fixation ability of chloroplasts increased from 8 to 15 d. CO₂ fixation ability of chloroplasts started to decline from base to apex of 15-d-old seedlings, where the content of ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (RuBPCO-LSU) increased acropetally. RuBPCO-LSU content was maximum in all the leaf segments in 12-d-old seedlings. This shows a distinctive pattern of PS2, Chl, CO₂ fixation ability of chloroplasts, and RuBPCO-LSU content along the axis of leaf lamina during development and senescence. RuBPCO-LSU (54 kDa) degraded to fragments of 45, 42, 37, 19, and 16 kDa products which accumulated along the leaf axis during ageing of chloroplasts. Thus the CO₂ fixation ability of chloroplasts declines earlier than PS2 activity and photosynthetic pigment contents along the leaf lamina.