Keratinocyte growth-promoting activity from human placenta

Extracts of term human placenta were tested for enhancement of proliferative growth of primary cultures of human keratinocytes. Saline extracts or supernatants from homogenates were dialyzed extensively, lyophilized, and tested in subcultures of keratinocytes in MCDB 153 medium with 0.1 mM Ca++ containing only defined supplements (insulin, hydrocortisone, transferrin, ethanolamine, phosphoethanolamine). Cells plated in the absence of EGF at moderately high densities (1000-3000 cells per cm2) formed colonies and grew in the presence of placental extract at 25-500 micrograms/ml. Extracts of cord serum or maternal serum were inactive, suggesting that the activity is derived from placental tissue. The activity is not EGF, since the activity in the placental extract, unlike EGF, did not promote growth at low cell density, was synergistic with EGF under some conditions, and did not produce changes in colonial morphology which occurred in the presence of EGF. Unlike keratinocyte growth-promoting activity in bovine hypothalamic extract, the activity is non-dialyzable and is destroyed at 100 degrees C. Placental extract could not replace any of the defined components of the medium and is therefore distinct from them. The presence of activity in the placenta with distinctive properties suggests that this is a previously undescribed material with growth-promoting properties for epithelium.     

EXO5-DNA structure and BLM interactions direct DNA resection critical for ATR-dependent replication restart

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Respiratory components in acidophilic bacteria that respire on iron

Abstract

Microorganisms capable of aerobic respiration on ferrous ions are spread throughout eubacterial and archaebacterial phyla. Phylogenetically distinct organisms were shown to express spectrally distinct redox‐active biomolecules during autotrophic growth on soluble iron. A new iron‐oxidizing eubacterium, designated as strain Funis, was investigated. Strain Funis was judged to be different from other known iron‐oxidizing bacteria on the bases of comparative lipid analyses, 16S rRNA sequence analyses, and cytochrome composition studies. When grown autotrophically on ferrous ions, Funis produced conspicuous levels of a novel acid‐stable, acid‐soluble yellow cytochrome with a distinctive absorbance peak at 579 nm in the reduced state.

Stopped‐flow spectrophotometric kinetic studies were conducted on respiratory chain components isolated from cell‐free extracts of Thiobacillus ferrooxidans. Experimental results were consistent with a model where the primary oxidant of ferrous ions is a highly aggregated c‐type cytochrome that then reduces the periplasmic rusticyanin. The Fe(II)‐dependent, cytochrome c‐catalyzed reduction of the rusticyanin possessed three kinetic properties in common with corresponding intact cells that respire on iron: the same anion specificity, a similar dependence of the rate on the concentration of ferrous ions, and similar rates at saturating concentrations of ferrous ions