High affinity binding of divalent cation to actin monomer is much stronger than previously reported

Monomeric actin is known to bind tightly one divalent cation per molecule. We have quantitatively reinvestigated the affinity of actin for Ca++ and Mg++ using the fluorescent Ca++ chelator Quin2 to induce and measure the dissociation of Ca++ from Ca-actin, supporting these studies with measurements using 45Ca. We found that the KD for Ca-actin is actually 1.9 +/- 0.7 nM. Kinetic analysis supported this result and demonstrated a dissociation rate constant (k-) of 0.013 s-1 and an association rate constant (k+) of 6.8 X 10(6)M-1 s-1 for Ca-actin. Competitive binding studies indicated that the binding affinity of actin for Ca++ is 5.4 times that for Mg++, yielding a calculated KD for Mg-actin of about 10 nM. Thus, the tight-binding of divalent cations to actin is 3-4 orders of magnitude stronger than previously thought.     

Human serum does contain a high molecular weight hepatocyte growth factor: studies pre- and post-hepatic resection

Levels of a high molecular weight hepatotrophin were measured in human serum taken from patients before and 24 hours after undergoing major hepatic resection. In in-vitro rat hepatocyte cultures a 'hepatotrophin' enriched fraction of human serum induced the incorporation of tritiated thymidine into DNA in both pre and post-operative patients. Levels after hepatic resection were 2-3 fold higher than those achieved at the same protein concentration before operation in the same patient. The hepatotrophic factor had an apparent molecular weight of approximately 150,000 daltons, and was an anionic protein.     

Comparison of patterns of hybrid resistance to the BALB/c plasmacytomas LPC-1 and MPC-11

Summary Patterns of genetic control of hybrid resistance to the BALB/c plasmacytoma LPC-1 were studied for comparison with those to MPC-11, a plasmacytoma investigated previously. The overall patterns of hybrid resistance to the two tumors were similar, i.e., hybrids between BALB/c and BALB congenic resistant (CR) strains, A and A CR strains, SJL and DBA/2 were as susceptible to LPC-1 as BALB/c mice themselves, whereas hybrids between BALB/c and AKR, C57BL/Ks, DBA/1, C57BL/6 (B6), C57BL/10 (B10) and B10 CR strains were resistant to LPC-1 as previously shown with MPC-11. Heterozygosity within the H-2 complex alone was insufficient for resistance to either tumor. Among hybrids between BALB/c and the B10 CR strains, however, the presence of certain H-2 haplotypes influenced the degree of resistance seen and this H-2 effect was different for the two tumors. A sex effect on resistance to LPC-1, but not to MPC-11, was seen among F₁ hybrids between BALB/c and DBA/1 although not in any other F₁ hybrids. Among ((B10×BALB/c)F₁×BALB/c) and (BALB/c×(B10×BALB/c)F₁) and ((BALB/c×B10)F₁×BALB/c) and ((BALB/c×B10)F₁×BALB/c) backcross mice, however, significantly more males than females were resistant to LPC-1 and the results of this study are compatible with the idea that in F₁ hybrids between BALB/c and B10, resistance to LPC-1 is controlled by two dominant autosomal genes, one of which is sex-limited and neither of which is linked to H-2. In contrast, hybrid resistance to MPC-11 in this cross is controlled by a single gene. Cross-protection experiments indicated that the two tumors share at least one tumor-associated transplantation antigen.     

Transfer RNA genes ofZea mays chloroplast DNA

A minimum of 37 genes corresponding to tRNAs for 17 different amino acids have been localized on the restriction endonuclease cleavage site map of theZea mays chloroplast DNA molecule. Of these, 14 genes corresponding to tRNAs for 11 amino acids are located in the larger of the two single-copy regions which separate the two inverted copies of the repeat region. One tRNA gene is in the smaller single-copy region. Each copy of the large repeated sequence contains, in addition to the ribosomal RNA genes, 11 tRNA genes corresponding to tRNAs for 8 amino acids. The genes for tRNA₂ ^Ile and tRNA^Ala map in the ribosomal spacer sequence separating the 16S and 23S ribosomal RNA genes. The three isoaccepting species for the tRNAs^Leu and the three for tRNAs^Ser, as well as the two isoaccepting species for tRNA^Asn, tRNA^Gly, tRNAs^Ile, tRNAs^Met, tRNAs^Thr, are shown to be encoded at different loci. Two independent methods have been used for the localization of tRNA genes on the physical map of the maize chloroplast DNA molecule: (a) cloned chloroplast DNA fragments were hybridized with radioactively-labelled total 4S RNAs, the hybridized RNAs were then eluted, and identified by two-dimensional polyacrylamide gel electrophoresis, and (b) individual tRNAs were³²P-labelledin vitro and hybridized to DNA fragments generated by digestion of maize chloroplast DNA with various restriction endonucleases.     

Cephalexin and Cephaloglycin Activity In Vitro and Absorption and Urinary Excretion of Single Oral Doses in Normal Young Adults

A large number of recently isolated bacterial pathogens were tested for susceptibility to cephalexin and cephaloglycin by the replica inoculating method. Strains of group A hemolytic streptococci, viridans (alpha and gamma) streptococci, pneumococci, gonococci, meningococci, and penicillin G-sensitive Staphylococcus aureus were all moderately to highly susceptible to both of these cephalosporin analogues, nearly all of the strains being two to eight (median four) times more susceptible to cephaloglycin than to cephalexin. The penicillin G-resistant, penicillinase-producing strains of S. aureus varied in their susceptibility; many were moderately resistant to both analogues, particularly to cephalexin. Strains of enterococci, Haemophilus influenzae, and most of the common gram-negative bacilli were moderately to highly resistant. Reducing the size of the inoculum had variable effects on inhibition by these drugs, depending on the species or strain. The activity of cephalexin was very little affected by pH of the medium within the clinical range or by incubation at 37 C in broth for up to 24 hr. In contrast, cephaloglycin in broth deteriorated rapidly at 37 C, and its activity was markedly reduced in alkaline medium. Both cephalexin and cephaloglycin were rapidly absorbed and excreted into the urine after single oral doses of 500 mg. Much higher levels were achieved and sustained with the former. Absorption of both analogues was delayed when taken with food, and the levels in the serum were significantly higher and better sustained when probenecid was also given. Very high concentrations of cephalexin were excreted into the urine during the first 4 hr, and the levels were still high in the 4- to 8-hr collection. The concentrations of cephaloglycin in the urine at these times were much lower. An average of 80 to 93% of the dose of cephalexin and 25 to 30% of the cephaloglycin were accounted for as active drug in the urine collected in 8 hr. Both analogues were well tolerated.     

Carotenoids of Thiorhodaceae

Summary The isolation, morphology and growth chracteristics of pure cultures of a Thiothece, Lamprocystis and Thiodictyon strain are described.Their carotenoid composition is reported. The Thiothece strain produced in addition to okenone (1), several related ketocarotenoids, among which a demethylated okenone (6) was identified by a small scale total synthesis. Thiodictyon and Lamprocystis produced carotenoids of the rhodopinal (previously warmingone) series, the latter organism contained as major carotenoids a lycopenol (4), not previously found in Nature, and a cross-conjugated lycopenal (2), previously called anhydro-warmingone.Part 7. Acta chem. scand. 21, 2185 (1967).     

Sex-related Resistance in Hamsters to Adenovirus-12 Oncogenesis II. Influence of Virus Dose

A significantly higher proportion of female hamsters developed tumors than did males given the same dose of adenovirus-12 (Huie) at birth over a dose range from 10(5.0) to 10(7.0)tcd(50) for human embryonic kidney cells. The 50% tumor dose (td(50)) was calculated to be 10(5.90)tcd(50) for females and 10(6.27) for males. Tumor response patterns induced with approximate td(50) inocula, 10(6.0) for females and 10(6.3) for males, were quite similar. The greater susceptibility of females was not found to be characteristic of a single strain of hamsters; nor was it attributable to a single lot of virus, to a single type of human cell used to produce the virus, nor to the degree of purification of the virus inoculum. The inoculation route did not appear to be of importance. Inasmuch as the foregoing extrinsic factors were of little influence, it was concluded that the mechanism is host-mediated, presumably hormonally controlled. The possibility that female cells, independent of host control, are more susceptible to adenovirus-12 oncogenesis than male cells has not been explored. Tumor regression occurred in 20% of the 211 tumors in males and in 15% of the 355 tumors in females. Adenovirus-12 T-antibody was detected in all but six of 473 sera tested from tumor-bearing hamsters and in 50% of 94 sera tested from non-tumor-bearing animals given virus at birth. Antibodies in the latter group were detected almost exclusively by indirect immunofluorescence. This technique appears to be extremely sensitive for detection of low levels of adeno-12 T-antibodies. The implications of T-antibody in nontumor-bearing virus-injected hamsters are discussed. Sera from normal hamsters were free of T-antibody.     

REVERSIBLE DEACTIVATION OF NEUROSPORA ASCOSPORES BY LOW TEMPERATURE

Sun, Clare Y., and Alfred S. Sussman. (U. Michigan, Ann Arbor.) Reversible deactivation of Neurospora ascospores by low temperature. Amer. Jour. Bot. 47(7): 589-593. Illus. 1960.—Heat-activated ascospores of Neurospora tetrasperma are reversibly deactivated after incubation at 4°C. for 36–48 hr. Two cycles of deactivation and reactivation are possible although the percentage germination decreases in the last cycle. By contrast, spores held at 20°C., or in glycerol at 4°C., will remain activated for much longer periods of time. If an incubation period at 20°C. greater than 30 min. is interposed before the activated spores are placed at 4°C., germination occurs despite the cold-treatment. Furfural-activated ascospores, when held at 4°C., are deactivated but can be reactivated only by heat, pointing up a difference between ascospores activated by these different means. Although a fraction of the stimulus afforded by heat-sensitization to chemical activators is preserved for 2 days at —20°C., it is dissipated completely after a short time at 4°C. These data are discussed on the basis of the suggestion that the reversible production of a substance initiates a series of steps which lead to germination. Thus, the temperature minimum of the forward reaction is greater than 4°C. whereas the back reaction proceeds at this temperature.