Dihydrofolate reductase: low-resolution mass-spectrometric analysis of an elastase digest as a sequencing tool (Short Communication)

An elastase digest of a protein of unknown structure, dihydrofolate reductase, was studied by mass spectrometry. This soluble digest contained a large number of small peptides in different yields, within the ideal molecular-weight range (200-1200) for mixture-analysis mass spectrometry. Sequences of the major component peptides in the digest are reported.     

The transport and metabolism of 14C-labelled indoleacetic acid in intact pea seedlings

Summary Part of the IAA-I- or IAA-2-¹⁴C applied at low concentrations to the apices of intact, light-grown dwarf pea seedling was transported unchanged to the root system The calculated velocity of transport in the stem was 11 mm per hour. In the root the label accumulated in the developing lateral root primordia.A large proportion of the applied IAA was converted by tissues of the apical bud, stem and root to indole-3-acetyl-aspartic acid (IAAsp). This compound was not transported. In addition evidence was obtained for the formation of IAA-protein complexes in the apex and roots, but not in the fully-expanded internodes.Large quantities of a decarboxylation product of IAA, tentatively indentified as indole-3-aldehyde (IAld), and several minor metabolites of IAA, were detected in extracts of the roots and first internodes, but not in the above-ground organs exposed to light. These compounds were readily transported through stem and root tissues. Together, the decarboxylation of IAA and the formation of IAAsp operated to maintain a relatively constant level of free IAA-¹⁴C in the root system.     

Metabolism of Glutamic Acid and N-Acetylglutamic Acid in Leaf Discs and Cell-free Extracts of Higher Plants

Radioactive glutamic acid and N-acetylglutamic acid have been incubated with normal and wilted leaf discs and radioactivity recovered in uncombined proline. The discs which had been placed under moisture stress incorporated considerably more label in uncombined proline than did normal discs.     

Properties of the inactive ribosomal components in rat liver and hepatoma

1. The relative concentrations of the inactive ribosomal components were compared in normal and regenerating rat liver and in two transplantable rat hepatomas (hepatomas 7800 and 5123D). 2. The size of the ribosomal-subunit pools in normal liver was not significantly affected by partial hepatectomy or neoplasia although, as shown previously, significant changes do occur in the monomer pool. 3. Further, the subunit pools in both liver and hepatoma were not significantly influenced by several treatments that caused dramatic changes in the size of the ribosomal monomer (and dimer) pools. 4. The high concentration of inactive monomers and dimers in the hepatomas appears to arise from limitations at the translational level, since they can be incorporated into pre-existing polyribosomes under the influence of cycloheximide.     

Pathogenesis of Lethal Shock After Intravenous Staphylococcal Enterotoxin B in Monkeys

The pathogenesis of shock in the rhesus monkey given intravenous staphylococcal enterotoxin B (SEB) is not understood. Several cardiovascular changes produced by a highly purified preparation of SEB were studied after administration of doses ranging from 50 to 1,000 mug/kg. Irreversible arterial hypotension was found consistently at the higher doses. Arterial blood pressure and cardiac output declined substantially as shock developed. Total peripheral vascular resistance did not rise at any time, but showed a significant fall during the late stages of shock. Portal and central venous pressures remained essentially unchanged. Venous O(2) content and pO(2) declined gradually throughout the period of toxemia, but arterial O(2) content remained constant until just prior to death, when a slight fall was noted in some monkeys. These changes were consistent with a pooling of blood in the peripheral vascular beds and seemed to resemble cardiovascular responses reported to occur in monkeys during shock due to bacterial endotoxin. Epinephrine, administered in the late stages of shock, caused arterial pressure to increase almost immediately and cardiac output to return to normal about 1 min later. Although life could occasionally be prolonged for several hours by continuous or intermittent epinephrine infusions, this therapy never succeeded in reversing the lethal effects of high doses of SEB.     

Observations on the Occurrence, Distribution, and Seasonal Incidence of Blue-green Algal Viruses

Phycovirus populations were found in 11 of the 12 waste stabilization ponds studied. These populations were comprised solely of blue-green algal (BGA) viruses. Two virus types were observed, one of which was related to the previously reported LPP-1 virus. The incidence and magnitude of the LPP group indicated that several of the ponds supported well-established BGA virus populations of this type. Counts as high as 270 plaque-forming units/ml were noted; however, marked differences in the nature and magnitude of these BGA viruses were apparent even in geographically related ponds of similar design. Of the algal strains found dominant in these ponds, none was of the type reported susceptible to the LPP viruses.     

The Aerogenic Response of Escherichia coli and Strains of Aerobacter in EC Broth and Selected Sugar Broths at Elevated Temperatures

Gas formation by 116 strains of Escherichia coli and 104 strains of Aerobacter was determined in a specially constructed and accurately controlled water bath employing EC, lactose, maltose, sucrose, glucose, levulose, and galactose broths at temperatures ranging from 44.5 to 46.5 C.

Greatest gas activity occurred in EC broth. In the range 44.9 to 45.5 C over 92% of the E. coli cultures formed gas, but the Aerobacter strains dropped from 68 to 2%. A natural point of separation of the two groups occurred at 45.5 C.

Inhibition of the gas-forming mechanism rather than death is the universal response of the Escherichia organisms to these temperatures. The inhibition increases with rising temperatures and is readily reversible. At 46.5 C, 64.5% of all the Escherichia cultures were inhibited and 69.1% of all the cultures were actually viable.

In EC broth it was found that as a group atypical E. coli (-+--) were the most resistant gas-positive types. Least resistant in EC broth was a group of known typical fecal isolates of E. coli (++--). Of intermediate resistance between the two groups was the large body of typical E. coli (++--) organisms.

Certain individual strains of E. coli excelled in the production of gas in the variety of sugar broths tested at elevated temperatures. The Aerobacter strains did not exhibit this property.

Finally it is suggested that elevated temperature incubation studies of this type be conducted in critically controlled water baths with an ascertained accuracy in the vicinity of 45.5 ± 0.1 C under full load.