Formation of an infinite beta-sheet arrangement dominates the crystallization behavior of lambda-type antibody light chains

The packing interactions in crystals of human lambda-type antibody light chain dimers have been reviewed. These homologous proteins are composed of individually specific variable domains, but all have very similar constant domain sequences. The proteins do not emulate each other in their overall crystallization behavior: each attains an individually characteristic space group or unit cell dimensions. However, each of these protein crystals has one unit cell dimension in common, 72.4(+/- 0.2) A. Examination of the protein packing in these crystals reveals that the common cell dimension is a consequence of a packing arrangement of their constant domains, which is conserved in all three crystals. In this striking arrangement, beta-sheets of adjacent constant domains are placed in juxta-position to form an "infinite chain". Although this constant domain packing pattern is rigorously conserved, the variable domain packing arrangements in each of these crystals are different. The conservation of the "infinite" beta-sheet pattern suggests that the constant domain interactions dominate the thermodynamic energy of lattice formation, probably through a combination of specific hydrogen bond formations and by a decrease in the solvent-accessible surface. A single amino acid substitution prohibits this characteristic interneighbor hydrogen bond pattern in the homologous kappa-type light chains. This may explain the observation that very few kappa-type light chains have been crystallized.     

Alteration of Striatal Glutamate Release After Glutamine Synthetase Inhibition

The effect of the glutamine synthetase (GS) inhibitor, methionine sulfoximine (MSO), on glutamate levels in, and glutamate release from, rat striatal tissue was examined. Tissue levels of glutamate were unchanged 24 h after an intraventricular injection of MSO, but tissue glutamine levels were decreased 50%. Calcium-dependent, potassium-stimulated glutamate release was diminished in tissue prisms from animals pretreated with MSO compared to controls. The decreased release of glutamate correlated over time with the inhibition of GS following an intraventricular injection of MSO. The maximum diminution of calcium-dependent, potassium-stimulated glutamate release (50%) and the maximum inhibition of GS activity (51%) were observed 24 h after MSO. The addition of 0.5 mM glutamine to the perfusion medium completely reversed the effects of MSO pretreatment on calcium-dependent, potassium-stimulated glutamate release. Since GS is localized in glial cells and the measured glutamate release is presumed to occur from neurons, the data support the contention that astroglial glutamine synthesis is an important contributor to normal neuronal neurotransmitter release.     

Absence of subtransition in racemic dipalmitoylphosphatidylcholine vesicles

dl-Dipalmitoylphosphatidylcholine multilamellar vesicle suspensions were examined by the method of differential scanning calorimetry. A lack of the subtransition at 18°C was established. Such a subtransition is characteristic for l-dipalmitoylphosphatidylcholine suspensions. This lack is supposed to be the result of the impossibility of the racemic phospholipid mixture to form the low-temperature crystal structure L_c.     

STUDIES ON LYMPHOCYTES

Some of the time parameters of the cell cycle in bovine thoracic duct lymphocytes have been estimated by analysing labeled mitoses curves, and by double labeling. The two methods gave similar estimates of T_s. Thus, T_s measured directly from labeled mitoses curves varied from 4 to 6 hr, while the estimates from double labeling were 4.8 and 4.5 hr. T _G measured directly from labeled mitoses curves was 5 hr, and estimates of T_G from the values of T_s ranged from 6.3 to 7.7 hr. The present data confirm the short generative cycle of large thoracic duct lymphocytes. Extracorporeal irradiation of the lymph (ECIL) had no detectable effect on the cell cycle or the fractional production rate of the lymphocytes. However, the calculated absolute production was reduced following ECIL, due to a decrease in the absolute number of cells present. The grain count over mitoses after ECIL was approximately one-half that found before ECIL.     

Transduction of Merodiploidy: Induced Duplication of Recipient Genes

Escherichia coli PB160, which carries a tandem duplication with the gene order metB(+)argH(-)su(159) (+)thi(+): metB(+)argH(+)su(159) (-)thi(+), was used to study the mechanism of P1 transduction of genes in the duplicated region. Transduction of the su(159) (+) allele contained within the duplicated segment yields two kinds of su(159) (+) recombinants: 91% are haploid su(159) (+) and 9% are su(159) (+)/su(159) (-) merodiploids. The duplication in these merodiploid transductants includes the metB locus; however, both copies of the metB locus usually are derived from the recipient. Thus, the requirements for transduction of the "condition of merodiploidy" appear to be the cotransduction of the repeat point (the region where the duplication begins to repeat itself) and, of course, the selected marker (in this case su(159) (+)). A mechanism whereby two recipient chromosomes interact with the transduced "repeat point" region to regenerate the tandem duplication is implicated. It appears that a duplication much larger than the quantity of genetic material carried by a P1 phage can be produced in a transductant.     

Bacterial Interference with L-Forms

During the course of studying the effect of normal nasal flora on the growth of L-forms, a clear zone of inhibition was observed around colonies of many coagulase-negative staphylococci. Subsequent investigation demonstrated that Staphylococcus aureus and some S. albus strains produce a substance which is capable of markedly inhibiting the growth of stable staphylococcal and streptococcal L-forms. This interfering substance is separable from the staphylococcal organism and is diffusible through 1.5% agar, but not through a dialysis membrane. It is heat-stable.