PHOSPHOLIPID-SUGAR COMPLEXES IN RELATION TO CELL MEMBRANE MONOSACCHARIDE TRANSPORT

The relative roles of calcium, phosphorus, and parathyroid hormone in glucose- and tolbutamide-mediated insulin release

The relative contributions of Ca++, phosphorus, and parathyroid hormone (PTH) on insulin secretion were evaluated in three groups of dogs. Dogs were studied with glucose infusions (group I) or standard intravenous glucose tolerance tests (IVGTT) (group II) before and after the development of diet-induced hypophosphatemia. Mean serum phosphorus levels for both groups fell from 4.1 to 1.1 mg/100 ml. Animals in group I demonstrated a fall in glucose disappearance rates (Kg) from 5.3+/-0.6% min to 3.5+/-0.5% after induction of hypophosphatemia (P less than 0.001). Mean insulin response was significantly greater in the hypophosphatemic animals than in controls in this group. In group II animals, mean insulin areas obtained during the IVGTT increased from 1,426+/-223 to 2,561+/-141 muU/ml/60 min after induction of hypophosphatemia, and were unaffected by Ca++ or PTH administration. Ca++ administration, but not hypophosphatemia or PTH infusion, increased significantly the mean insulin response to tolbutamide. Secondary hyperparathyroidism was induced by dietary manipulation in four dogs (group III). Mean PTH values increased from 71.4+/-2.1 to 3,012+/-372 pg/ml (P less than 0.001). Mean insulin response to an IVGTT was similar to group III animals, but increased from 1,352+/-128 to 1,894+/-360 muU/ml/60 min after the excessive dietary phosphorus was reduced for 3 mo, and plasma phosphorus fell from 3.2+/-0.1 to 2.8+/-0.3 mg/100 ml. PTH values decreased to 647+/-53 pg/ml. The insulin response to tolbutamide was comparable to that in group II animals, but increased significantly after calcium administration. Immunoreactive insulin disappearance rates were unaffected by hypophosphatemia or diet-induced secondary hyperparathyroidism. These data demonstrate that hypophosphatemia is associated with an augmented glucose-stimulated insulin release, without any effect on tolbutamide-stimulated insulin release. Hypercalcemia produces an augmented tolbutamide-stimulated insulin release with no apparent effect on glucose-stimulated insulin release. Finally, PTH does not appear to be an insulin antagonist and has no apparent effect on either glucose- or tolbutamide-stimulated insulin release in animals with dietary-induced secondary hyperparathyroidism.

Phospholipids of Streptococcus faecalis

Autoradiograms of total lipid extracts from Streptococcus faecalis ATCC 9790, harvested in the stationary phase from a medium containing (32)P-orthophosphate, showed six major spots. The corresponding compounds were identified as diphosphatidylglycerol (possibly with a penta acyl structure); phosphatidylglycerol; a provisionally identified mixture of alanylphosphatidylglycerol and of the 2'-lysyl-derivative of phosphatidylglycerol; the 3'-lysyl-derivative of phosphatidylglycerol, probably together with some arginylphosphatidylglycerol; a diglucosyl derivative of phosphatidylglycerol; and a compound which was tentatively identified as the 2',3'-dilysyl derivative of phosphatidylglycerol.

Uptake of N-ethylmaleimide and I-Fluoro-2, 4-dinitrobenzene in relation to the irreversible inhibition of glucose transfer in the human erythrocyte

1. The uptake of the inhibitors N-ethylmaleimide (NEM) and 1-fluoro-2,4-dinitrobenzene (DNFB) by human red cells has been correlated with the inhibition of glucose exit.2. With both inhibitors there was an initial rapid uptake by the cells with little inhibition; this was followed by a phase when inhibition was developing rapidly but uptake continued at a steady rate even after the development of inhibition had flattened off.3. The rate of uptake of DNFB during the rapid development of inhibition corresponded to about 4 x 10(8) molecules/cell for 100% inhibition, irrespective of the temperature of incubation. This cannot be used as an estimate of the number of glucose transfer sites in the cell membrane because of the lack of specificity.4. In an examination of lipids from red cells incubated with [(14)C]DNFB, labelling associated with lipids was eluted with peaks in chloroform-methanol 4:1 and 1:4 respectively. Thus, although DNFB is normally regarded as a protein reagent, involvement of lipids in the transfer of glucose could not be excluded.

Water permeability of thin lipid membranes

The osmotic permeability coefficient, P(f), and the tagged water permeability coefficient, P(d), were determined for thin (<100 A) lipid membranes formed from ox brain lipids plus DL-alpha-tocopherol; their value of approximately 1 x 10(-3) cm/sec is within the range reported for plasma membranes. It was established that P(f) = P(d). Other reports that P(f) > P(d) can be attributed to the presence of unstirred layers in the experimental determination of P(d). Thus, there is no evidence for the existence of aqueous pores in these thin phospholipid membranes. The adsorption onto the membrane of a protein that lowers its electrical resistance by a factor of 10(3) was found not to affect its water permeability; however, glucose and sucrose were found to interact with the membrane to modify P(f). Possible mechanisms of water transport across these films are discussed, together with the implications of data obtained on these structures for plasma membranes.

EFFECT OF BIOTIN ON FATTY ACID DISTRIBUTION IN ESCHERICHIA COLI

Gavin, John J. (Rutgers, The State University, New Brunswick, N.J.), and Wayne W. Umbreit. Effect of biotin on fatty acid distribution in Escherichia coli. J. Bacteriol. 89:437-443. 1965.-Biotin deficiency causes changes in the composition and distribution of the fatty acids in cell wall-cell membrane fractions of Escherichia coli T 94A. Most notable among the fatty acid changes are decreased amounts of unsaturated fatty acids, the presence of unsaponifiable lipid material, and the lack of a lipopolysaccharide fraction in the cell wall-cell membrane. Also, though the hexane-extractable material from the lipoprotein fraction of biotin-adequate cells will transfer glucose from water to hexane, the same material from biotin-deficient cells will not.