The tartrolons, new boron-containing antibiotics from a myxobacterium, Sorangium cellulosum

New antibiotics were isolated from the culture broth of the myxobacterium, Sorangium cellulosum, strain So ce 678. The antibiotics were active against Gram-positive bacteria and mammalian cells. They were named tartrolon A and B. Tartrolon B contains a boron atom. The boron binding region of tartrolon is identical with that of boromycin and aplasmomycin.

On the application of the Clark oxygen electrode to the study of enzyme kinetics in apolar solvents: the catalase reaction

A method for recording O2 concentrations in nonconducting organic media with the Clark oxygen electrode was developed. Spontaneous oxidation of Na2S2O4 and the enzymatic reduction of NaBO3 or H2O2 by bovine liver catalase trapped in hydrated micelles of dioctylsulfosuccinate (AOT)/toluene were used as model systems. O2 titration with the above systems showed that air-saturated 1.6 M H2O/0.2 M AOT/toluene media contain seven times more O2 (1.4 mM) than aqueous solutions (0.2 mM). The measured Km values of catalase for NaBO3 and H2O2 in organic media were Kmov = 15 and 17 mM, respectively, whereas in aqueous buffer the values were 45 and 54 mM. In the toluene media, catalase activity increased with the W0 (H2O/AOT molar ratio) of the micellar preparation, reaching maximal activity at W0 = 10-12; under this condition, the catalytic center activity (Kp) of H2O2 was 7 x 10(6) min-1, similar to that obtained in the aqueous buffer (H2O2 = 7 x 10(6) min-1). It was found that the optimal pH for catalase in toluene media (pH 8.0) was shifted 1.0 unit compared to that in the aqueous buffer (pH 7.0). On the other hand, catalase was severely inhibited by NaN3 in both media. Thus, polarography based on the Clark oxygen electrode seems to be an easy, rapid, and sensitive technique for studying enzyme reactions consuming or evolving O2 in apolar media.

The interaction of anions with native and phenylglyoxal-modified human serum transferrin

The interaction of various anions with human serum transferrin was investigated due to the concomitant binding of iron and a synergistic anion to form the transferrin-anion-iron complex. Two tetrahedral oxyanion oxidizing agents, periodate and permanganate, were found to partially inactivate transferrin when used at equimolar ratios of oxidizing agent to protein active sites. Hypochlorite, a strong oxidizing agent with little structural similarity to periodate and permanganate, had little effect on iron-binding activity when used at similar low molar ratios of reagent to transferrin active sites. Transferrin treated with a 3:1 molar ratio of periodate or permanganate to active sites lost 74 or 67% of its iron-binding capacity, respectively. The composition of the buffer affected the extent of transferrin inactivation by periodate and permanganate; for example, the extent of inactivation by periodate was threefold greater in a borate buffer than in a phosphate buffer. Comparative oxidations in buffer systems suggest the following order of affinity of three buffer anions for the apotransferrin metal-binding center: phosphate greater than bicarbonate greater than borate. The interaction of phosphate ions with the iron-transferrin complex was also examined due to the increased susceptibility to periodate inactivation of iron-saturated transferrin in phosphate buffer (M. H. Penner, R. B. Yamasaki, D. T. Osuga, D. R. Babin, C. F. Meares, and R. E. Feeney (1983) Arch. Biochem. Biophys. 225, 740-747). The apparent destabilization of the iron-transferrin complex in phosphate buffer was found to be due to the competitive removal of iron by phosphate from the iron-protein complex. We found that phenylglyoxal-modified Fe-transferrin, with no loss of bound iron, was much more resistant to iron removal by phosphate and other competitive chelators.

The specificity and kinetic properties of trypsin ethylated at the binding site

Treatment of trypsin with triethyloxonium tetrafluoroborate at pH 8, 25 degrees C, results in abolition of binding to the enzyme of specific cationic substrates and inhibitors. The binding constant of soybean trypsin inhibitor to ethylated trypsin is 10000-fold smaller than to intact trypsin. However, the intrinsic ability of trypsin to recognize and react with nonspecific neutral substrates and inhibitors is not lost, and in several cases even considerably enhanced. Thus ethylated trypsin (Tret) resembles chymotrypsin in its behavior. Trypsin-like enzymes are also affected in a similar manner.

Palytoxin both induces and inhibits the release of histamine from rat mast cells

Palytoxin (PTX) is a potent releaser of histamine from rat mast cells. The concentration response curve is bell-shaped with its range between 0.05 ng/ml and 5 micrograms/ml and its maximum at 50 ng/ml. The release of histamine by PTX is specific because (a) heat-inactivated (50 degrees C) mast cells are insensitive to PTX, and (b) extracellular calcium is essential. Removal of extracellular potassium as well as the presence of borate shifts the curve to the left by factor of 10. At higher concentrations (5 micrograms/ml), PTX inhibits the release of histamine due to compound 48/80, MCD-peptide, Con-A, ionophore A-23187, and PTX itself.

Absorption of boron after mouthwash treatment with Bocosept

Healthy volunteers and patients with gingivitis were treated locally with the boron-containing bacteriostatic agent, Bocosept. Blood levels and urinary excretion of boron were examined by a spectrophotometric method. Blood concentrations after a single mouthwash with Bocosept slightly exceeded those after intake of 200 g raisins or a bottle of red wine. The blood levels during a one-week course of treatment showed a low rate of boron accumulation. The highest concentration was about 0.3 microgram B/ml, a level which does not seem to involve any risk of boron poisoning. The small amount taken up after mouthwash treatment with Bocosept does not appear to represent absorption by the oral mucosa. It seems more likely that the uptake of boron takes place in the intestine after ingestion of residual amounts from the mouth.

Pyridoxal phosphate. An anionic probe for protein amino groups exposed on the outer and inner surfaces of intact human red blood cells

Pyridoxal phosphate is a potent probe for exploring the "sidedness" of proteins in the membrane of the intact red blood cell. It reacts with amino groups with a high degree of specificity, forming a Schiff's base that can be fixed as an irreversible bond upon reduction with NaBH4; its binding site can be identified by use of [3-H]pyridoxal phosphate or NaB3-H4; it can be used as a surface probe under conditions of minimal penetration, or it can be used as a probe for proteins on the inside of the membrane under conditions of substantial uptake. Pyridoxal phosphate uptake involves a rapid and a slow component. The former represents the binding to the outer surface of the membrane; it is not substantially affected by pH and temperature, but is reduced considerably by pretreatment of cells by 4,4-diisothiocyano-2,2-stilbenedisulfonic acid, a specific inhibitor of anion transport. The slow component represents penetration into the cell; it is blocked by high pH, low temperature, or pretreatment with the disulfonic stilbene. Pyridoxal phosphate itself is also an effective and specific inhibitor of the permeation of other anions. Under conditions of minimal uptake, the only labeled proteins are three glycoproteins and a protein of apparent molecular weight 95,000. Under conditions of substantial uptake into the cell, the other major protein bands seen by staining on acrylamide gels after electrophoresis are labeled. It is concluded that virtually all of the major membrane proteins interact with pyridoxal phosphate from one side of the membrane or the other. The differences in labeling under conditions of minimal or maximal uptake can, therefore, be attributed to the sidedness in the distribution of the membrane proteins rather than to differences in their reactivity.

Boron in plants: a biochemical role

Boron, as borate, appears to have a role in partitioning metabolism between the glycolytic and pentose-shunt pathways. This effect results from the association of borate with 6-phosphogluconic acid, forming a virtual substrate that inhibits the action of 6-phosphogluconate dehydrogenase. In the absence of borate, the inhibition of the enzyme is released, and excess phenolic acids are formed. These acids also associate strongly with borate and thus develop an autocatalytic system for production of excess phenolic acids which cause necrosis of tissue and eventual death of the plant.