Degradation of mutagens from pyrolysates of tryptophan, glutamic acid and globulin by myeloperoxidase.

Mutagenic compounds isolated from pyrolysates of tryptophan, glutamic acid and globulin were broken down by myeloperoxidase and hydrogen peroxide with loss of their mutagenicity toward Salmonella typhimurium TA98. Lactoperoxidase and horseradish peroxidase were as effective as myeloperoxidase in degradation of the mutagens.     

Genetics of formamidase-5 (brain formamidase) in the mouse: Localization of the structural gene on chromosome 14

A single formamidase, which is different from the formamidases found in other tissues, occurs in the brains of mice. This enzyme is here called formamidase-5 and the gene symbol is designated For-5. Two alleles are recognized on the basis of their differential heat sensitivity: For-5 ^b is relatively heat stable and is present in strain C57BL/6J, while For-5 ^d is relatively heat sensitive and is present in strain DBA/2J. The heat sensitivity of formamidase-5 in 44 other inbred strains and substrains was tested and found to resemble that of C57BL/6J or DBA/2J. Thirty-six recombinant inbred strains derived from progenitors that differed at For-5 were studied to test for single-gene inheritance and linkage with other loci. Complete concordance was found with the esterase-10 locus (Es-10), indicating close linkage. The 99% upper confidence limit of the distance between For-5 and Es-10 is 3.7 centimorgans (cM). Es-10 is located on chromosome 14 about 19 cM from the centromere. An independent demonstration of linkage of For-5 with Es-10 and another chromosome 14 marker, hairless (hr), is provided by the finding that the HRS/J strain, which has been sibmated for 60 generations with forced heterozygosity at the hr locus, is cosegregating at For-5 and Es-10. A survey of 32 inbred strains and substrains revealed that the For-5 ^d allele is associated with the Es-10 ^b allele, and that the For-5 ^b allele is associated with Es-10 ^a and Es-10 ^c. Formamidase-5 segregates as expected in the F₂ generation of crosses between strains bearing For-5 ^b and For-5 ^d alleles. It is possible that this unique formamidase of the brain is involved in the metabolism of a neurotransmitter substance.This research was sponsored in part by the Department of Energy under contract with the Union Carbide Corporation and in part by NIH Research Grant GM-18684 from the National Institute of General Medical Sciences. J. C. F. is a predoctoral Fellow supported by Grant CA 09104 from the National Cancer Institute. The Biology Division of Oak Ridge National Laboratory and the Jackson Laboratory are fully accredited by the American Association for Accreditation of Laboratory Animal Care.     

Inhibition of modulation of thymus-leukemia antigens by concanavalin A.

When incubated at 37 °C in medium containing antibodies specific for thymus-leukemia (TL) antigens, viable cells bearing these antigens become resistant to the cytolytic effects of guinea pig complement, a process termed antigenic modulation. Antibody-induced membrane redistribution of the TL antigens, detected by indirect immunofluorescence, occurs with a similar pace. When high concentrations of concanavalin A (Con A) were included with antibodies in the incubation medium, TL antigenic modulation as well as antigen patching and capping were markedly inhibited, similar to effects of Con A on membrane immunoglobulin redistribution with murine spleen cells. Colchicine antagonized the inhibition by Con A suggesting the involvement of microtubules. In parallel experiments high concentrations of Con A failed to alter the quantity of TL antigen expression or its rate of change with time during incubation in cognate antisera. These results support the hypotheses that (a) generalized alterations in membrane receptor mobility may be induced by ligand binding to the cell membrane, and (b) under certain conditions stable interactions occur between normally independent cell surface antigens.     

Colorimetric determination of acetaldehyde in the presence of formaldehyde

A procedure is described that enables use of the p-phenylphenol color reaction to determine acetaldehyde in the presence of formaldehyde. The sample is first treated with an acidic 2,4-pentanedione reagent, which selectively removes formaldehyde. The method is applicable to blochemical reactions using tissue preparations.     

NMR of fd coat protein

The conformations of the major coat protein of a filamentous bacteriophage can be described by nuclear magnetic resonance spectroscopy of the protein and the virus. The NMR experiments involve detection of the ¹³C and ¹H nuclei of the coat protein. Both the ¹³C and ¹H nuclear magnetic resonance (NMR) spectra show that regions of the polypeptide chain have substantially more motion than a typical globular protein. The fd coat protein was purified by gel chromatography of the SDS solubilized virus. Natural abundance ¹³C NMR spectra at 38 MHz resolve all of the nonprotonated aromatic carbons from the three phenylalanines, two tyrosines, and one tryptophan of the coat protein. The α carbons of the coat protein show at least two different classes of relaxation behavior, indicative of substantial variation in the motion of the backbone carbons in contrast to the rigidity of the α carbons of globular proteins. The ¹H spectrum at 360 MHz shows all of the aromatic carbons and many of the amide protons. Titration of a ¹H spectra gives the pKas for the tyrosines.     

A calcitonin-like action of prostaglandin E1

The pharmacological effects of PGE₁ (6 and 9 days, 21,250 μg/kg per day subcutaneously) upon the growth and the bone resorption of mammals were studied using the proximal tibia and upper incisor of immature rats along with lead acetate as a time marker, and upon the serum calcium and inorganic phosphorus levels. The following results were obtained. 1. PGE₁ hardly affected the body weight or the weight of organs of the rats but apparently inhibited the longitudinal growth of proximal tibia in a dose related manner. 2. PGE₁ clearly inhibited not only the longitudinal growth (incisor growth) but also the appositional growth (dentin formation) of incisal dentin. 3. The grade of the inhibitory effect on the growth was in the order of bone growth >dentin formation >incisor growth. 4. The occurrence of osteoporosis due to a low calcium diet was inhibited by the simultaneous administration of PGE₁, the mechanism being considered to be mainly due to the inhibitory effect on the bone resorption. 5. PGE₁ lowered the level of serum calcium and the lowering effect was not observed in the thyro-parathyroidectomized rat. From the facts that the above effects were exactly the same as those of calcitonin (1), the possibility that the subcutaneous injection of PGE₁ may induce a calcitonin-like action, a part of which may dependent on the calcinonin secretion is suggested.     

Sensitivity of cultured rat hepatocytes to aflatoxin B1 and benzo(a)pyrene

Summary We have tested the sensitivity of a cloned rat hepatocyte line, RL-PR-C, to aflatoxin B₁ and benzo(a)pyrene as a function of population-doubling level. The cells were much more sensitive to the cytotoxic action of these agents subsequent to 230 population doublings. This sensitivity corresponded to the enhanced inducibility of arylhydrocarbon hydroxylase activity by 3-methylcholanthrene. Supported by Grants CA 21258 and CA 12056 from the National Cancer Institute.     

Maternal X chromosome expression in mouse chorionic ectoderm

An electrophoretic variant of the X-linked enzyme phosphoglycerate kinase (PGK-1) has been used to study regulation of X chromosome expression in the diploid derivatives of the trophectoderm at 8–8.5 days post coitum in the mouse. These derivatives included the chorionic ectoderm and the polar trophoblast. The biochemical analysis suggests that only the maternally derived X chromosome (X^m) is expressed in the diploid trophectoderm derivatives. Cell selection and maternal tissue contamination were ruled out as possible causes of the observed X^m expression. From these and other results, we conclude that all derivatives of the trophectoderm, along with the primitive endoderm, express only X^m, whereas derivatives of the primitive ectoderm show random X chromosome expression.