Differential inhibition and activation of two leaf dihydroxyacetone phosphate reductases : role of fructose 2,6-bisphosphate.

The chloroplastic and cytosolic forms of spinach (Spinacia oleracea cv Long Standing Bloomsdale) leaf NADH:dihydroxyacetone phosphate (DHAP) reductase were separated and partially purified. The chloroplastic form was stimulated by dithiothreitol, reduced thioredoxin, dihydrolipoic acid, 6-phosphogluconate, and phosphate; the cytosolic isozyme was stimulated by fructose 2,6-bisphosphate but not by reduced thioredoxin. End product components that severely inhibited both forms of the reductase included lipids and free fatty acids, membranes, and glycerol phosphate. In addition, two groups of inhibitory peptides were obtained from the fraction precipitated by 70 to 90% saturation with (NH(4))(2)SO(4). Chromatography of this fraction on Sephadex G-50 revealed a peptide peak of about 5 kilodaltons which inhibited the chloroplastic DHAP reductase and a second peak containing peptides of about 2 kilodaltons which inhibited the cytosolic form of the enzyme. Regulation of the reduction of dihydroxyacetone phosphate from the C(3) photosynthetic carbon cycle or from glycolysis is a complex process involving activators such as thioredoxin or fructose 2,6-bisphosphate, peptide and lipid inhibitors, and intermediary metabolites. It is possible that fructose 2,6-bisphosphate increases lipid production by stimulating DHAP reductase for glycerol phosphate production as well as inhibiting fructose 1,6-bisphosphatase to stimulate glycolysis.

Dihydroxyacetone phosphate reductase in plants.

Two forms of dihydroxyacetone phosphate reductase are present in spinach, soybean, pea, and mesophyll cells of corn leaves. An improved homogenizing medium was developed to measure this activity. The enzyme was detectable only after dialysis of the 35 to 70% saturated (NH(4))(2)SO(4) fraction and the two forms were separated by chromatography on either DEAE cellulose or Sephacryl S-200. About 80% of the reductase was one form in the chloroplast and the rest was a second form in the cytosol as determined by chromatography and by fractionation of subcellular organelles. The amount of activity detectable in the chloroplast fraction was 10.7 micromoles of dihydroxyacetone phosphate reductase per hour per milligram chlorophyll from spinach leaves and 4.9 from pea leaves. The chloroplast form eluted first from DEAE cellulose and, being smaller, it eluted second from Sephacryl S-200. Activity of the chloroplast form was stimulated 3- to 5-fold by the addition of 1 millimolar dithiothreitol or 50 microgram reduced Escherichia coli thioredoxin or 4 micrograms spinach thioredoxin to the assay mixture. This stimulation was not observed with monothiols. Activity of the cytosolic form was not affected by either reduced thioredoxin or dithiothreitol.

The epidemiology of hypertension in the South Pacific.

A review of published reports shows that in many South Pacific populations blood pressure does not rise with age. This contrasts with Western societies where hypertension and coronary heart disease are major health problems. There is evidence that hypertension is now becoming a problem in some Pacific societies and this seems to be related to increasing urbanization and westernization.

Australia and exotic animal diseases.

The Australian economy is vitally dependent on agriculture, livestock health and freedom from major exotic animal diseases. Future exotic animal disease pressures on Australian livestock industries will increase. High category risks include vesicular diseases, arthropod-borne virus diseases and Newcastle disease. Tighter quarantine control and surveillance alone cannot neutralise the increasing risks. Increasing preparedness to deal promptly with introduced disease demands a national approach and continuing liaison between veterinary authorities, the livestock industries and the many organisations that would be called on to assist in a major eradication effort.

The epidemiology of spinal cord injuries in Papua New Guinea.

Thirty six patients with traumatic spinal cord injury were studied in Papua New Guinean hospitals. Road trauma and falls from trees each accounted for 1/3 of injuries. The mean age of patients, 80% of whom were male, was 26 years. Complications included pressure sores (69%), urinary tract infection (61%) and contractures (22%). Two thirds of patients failed to make any significant recovery and remained permanently in hospital. At present there are no special facilities for treating paraplegic patients in this country but as the number of cases is increasing it is recommended that major hospitals provide special units and a standard management protocol for these patients.