Solar radiation incident on the Martian surface

Summary Calculations indicate that the maximum daily solar radiation reaching the Martian surface is about 325 cal/cm² during southern hemisphere summer at latitude of about 40°S. In the ultraviolet region of the spectrum, the radiation reaching the surface at wavelengths greater than 2800 Å is within 10% of the radiation incident on the atmosphere. There is significant extinction of radiation in the spectral region near 2500 Å in mid and high latitudes due to absorption of radiation by ozone; radiation reaching the surface may be reduced to one one-thousandth of that incident on the atmosphere during winter. Virtually no radiation of wavelengths less than 1900 Å reaches the surface because of absorption by the large column abundance of carbon dioxide. Daily and latitudinal distributions of radiation are presented for wavelengths of 3000, 2500 and 2000 Å.     

Genetic control of chalcone isomerase activity in anthers of Petunia hybrida

The gene Po in pollen of Petunia hybrida Vilm. controls a discrete step in flavonoid biosynthesis. In recessive genotypes, naringenin-chalcone (4, 2,4,6-tetrahydroxychalcone) is accumulated, whereas, under the influence of the wild-type allele flavonols and anthocyanins are formed. Enzymic investigations on anthers of four genetically defined lines with different pollen colouration revealed a clear correlation between accumulation of naringenin-chalcone and deficiency of chalcone isomerase (EC 5.5.1.6). The results allow the conclusion that chalcone is the first product of the flavanone synthase reaction in anthers of Petunia hybrida and that chalcone isomerase is essential for the formation of flavonols and anthocyanins. These results were similar to those previously obtained with Callistephus chinensis (L.) Nees.Abbreviations EGME ethylen glycol monomethyl ether - MeOH methanol - CI chalcone isomerase - HOAc acetic acid - TLC thinlayer chromatography     

Composition, stability and electrolyte permeability of Golgi membranes from lactating-rat mammary gland.

1. Golgi membrane vesicles, isolated from lactating-rat mammary gland and greatly enriched in galactosyltransferase (EC 2.4.1.22), contained over 40 separate bands of protein, including some periodic acid)(Schiff-staining material and free thiol groups, when analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. 2. The membrane lipids were enriched in phosphatidylcholine, phosphatidylethanolamine and unesterified cholesterol. 3. Membrane fluidity, as monitored by the fluorescence polarization of 1,6-diphenylhexa-1,3,5-triene, increased linearly over 5-37 degrees C. 4. The vesicle membranes were impermeable to lactose over a wide pH range, but admitted electrolytes of molecular weight below about 300. 5. These properties are discussed with respect to other cellular membranes and the secretion of milk products.     

Structural alterations of tapetal cells in the retina of cats induced by prolonged treatment with chloroquine

Summary Cats were treated with high doses of chloroquine for one year during which the ocular fundus was periodically examined. After completion of the treatment, the tapetal cells were investigated by light and electron microscopy. Prolonged treatment with the retinotoxic drug chloroquine reduced the light reflection of the fundus, and examination by light and electron microscopy revealed a destruction of the rod-like structures in the cytoplasm of the tapetal cells.     

DNA synthesis at a fork in the presence of DNA helicases

In a mixture of Escherichia coli DNA polymerase III holoenzyme, single-strand-binding protein, artificially forked lambda bacteriophage DNA with primer annealed to the leading side of the fork, dNTPs and ATP, DNA synthesis is enhanced by helicase II, less so by helicases, I, III or rep protein of E. coli or T4 phage helicase. The effect of helicase II depends on ATP, it is enhanced by helicase III, and it is not observed using DNA polymerase I or T4 DNA polymerase. In the absence of dNTPs helicase II is less active than helicase I or T4 helicase in unwinding the forked DNA. We believe that helicase II both shifts the forks and stimulates DNA polymerase III. The results support the conclusion derived from previous studies that helicase II is part of the DNA-synthesizing system of E. coli.     

Structural and functional properties of the p60 proteins from different Listeria species.

The major extracellular protein p60 of Listeria monocytogenes seems to be required for this microorganism's adherence to and invasion of 3T6 mouse fibroblasts but not for adherence to human epithelial Caco-2 cells. Western blot analysis with polyclonal antibodies against p60 of L. monocytogenes indicated the presence of cross-reacting proteins in the culture supernatants of all Listeria species. Protein p60 of L. monocytogenes could restore adhesion of the L. monocytogenes mutant RIII (impaired in the synthesis of p60) to mouse fibroblasts more efficiently than that of Listeria grayi. The amino acid sequences of the p60-related proteins of L. innocua, L. ivanovii, L. seeligeri, L. welshimeri, and L. grayi indicated highly conserved regions of about 120 amino acids at both the N-terminal and the C-terminal ends. The middle portions of these proteins, consisting of about 240 amino acids, varied considerably. These parts include the repeat domain consisting of repetitions of Thr (T) and Asn (N) which was present only, albeit in different arrangements, in the p60 proteins of L. monocytogenes and L. innocua. The p60-related proteins of L. grayi, L. ivanovii, L. seeligeri, and L. welshimeri each contained an insertion of 54 amino acids which was absent in the p60 proteins of L. monocytogenes and L. innocua.     

The association of insulin-elicited phosphotyrosine proteins with src homology 2 domains.

The interactions of the phosphotyrosine (Tyr(P))-containing proteins in basal and insulin-stimulated 3T3-L1 adipocytes with src homology 2 (SH2) domains from phosphatidylinositol 3-kinase (PI3K), ras GTPase-activating protein (GAP), and phospholipase C gamma have been examined. The Tyr(P) forms of the insulin receptor and its 160-kDa substrate protein (pp160) associated with fusion proteins containing either or both the SH2 domains of PI3K, but not with fusion proteins containing the two SH2 domains of GAP or phospholipase C gamma. These results demonstrate a specificity for the association of the Tyr(P) form of the insulin receptor and pp160 with SH2 domains that parallels the reported effects of insulin on PI3K, GAP, and phospholipase C gamma in vivo. Immunoprecipitates of pp160 from the cytosol of insulin-treated, but not basal, 3T3-L1 adipocytes contained PI3K activity. Moreover, the Tyr(P) form of pp160 with associated PI3K activity migrated at 10 S on a sucrose velocity gradient, whereas the Tyr(P) form without associated activity migrated at 6 S. These findings indicate that the Tyr(P) form of pp160 associates directly with PI3K in vivo.     

Distinct domains of an oligotopic membrane protein are Sec-dependent and Sec-independent for membrane insertion.

Leader peptidase of Escherichia coli spans the plasma membrane twice with its amino terminus on the periplasmic surface of the membrane and its large carboxyl-terminal domain protruding into the periplasm. To monitor the transfer of the amino terminus of leader peptidase to the periplasm, we have constructed a fusion protein between the 18-residue amino-terminal periplasmic domain of Pf3 bacteriophage coat protein and the beginning of leader peptidase. We find that neither the SecA or SecY proteins nor a transmembrane electrochemical potential is required for insertion of the amino terminus, while the transfer of the carboxyl-terminal domain of leader peptidase has these requirements. The first 35 residues of leader peptidase, which include the first hydrophobic domain and the carboxyl-terminal positively charged cluster, are sufficient to insert the amino terminus. When positively charged residues are introduced before the first transmembrane segment, translocation of the amino terminus is abolished. These studies in protein membrane topogenesis, showing that there are different requirements for amino and carboxyl termini insertion, indicate that multiple mechanisms exist even within the same protein.