Identification of four classes of cell surface antigens appearing at gastrulation in sea urchin embryos

An antiserum to isolated membranes of gastrula-stage embryos of the sea urchin Lytechinus variegatus was characterized by absorption and cell agglutination specificities. The antiserum was found to recognize four distinct classes of antigens on the embryonic cell surface: (1) an early embryonic class or “maternal” class present from the earliest stages of development, (2) an embryonic class of antigens which appeared on all cells beginning at gastrulation, (3) a class of antigens present on ectoderm cells, and (4) a class of antigens present on endoderm cells. All four classes of antigens were shown indirectly to be synthesized on embryonic mRNA since a hybrid embryo of the cross Tripneustes ♀ × Lytechinus ♂ expressed all four classes of Lytechinus-specific antigens beginning at gastrulation. Each class was Lytechinus specific in that hybrid cells were agglutinated if beyond the beginning of gastrulation, while normal Tripneustes ♀ × Tripneustes ♂ cells were not agglutinated.     

Xanthine oxidase activity in rat serum after administration of homogenized bovine cream preparation

Rats were given a single dose of saline, saline supplemented with xanthine oxidase (XO), half cream and half milk (H/H) and H/H supplemented with XO. XO was determined by a spectrophotometric method at 297 nm in serum at 0, 2, 4 and 6 hours after administration. The method is rapid, reliable and compares favorably with reported assays. No significant difference was obtained between the two saline treatments. The XO activity in serum of animals receiving the H/H increased significantly at 2 hours and then decreased. The H/H supplemented with XO demonstrated a maximum activity in serum at 4 hours and then declined to a value similar to that of the H/H treatment and below the XO level at 0 time. The initial increase in XO activity in serum of rats receiving the H/H treatments may indicate that XO is absorbed in the gastrointestinal tract or that the H/H materials stimulated endogenous XO activity.     

Physiological effects of crude oil exposure in the striped mullet, Mugil cephalus

Juvenile mullet ($\text{Mugil cephalus}$) were exposed to a surface slick of Empire Mix crude oil for a three week period in a simulated estuarine ecosystem. Liver weight to body weight ratios were increased in the mullet from the oil-treated ponds when compared to those from the control ponds. Activities of alkaline phosphatase, which were elevated in gill and muscle of oil-treated mullet, and β-glucuronidase, which was elevated in the muscle of oil-treated mullet, may be related to the degree of stress the animals were experiencing. Malic dehydrogenase, which was depressed in the livers and elevated in the muscle of oil-treated organisms, indicate changes in aerobic metabolism in response to the stress of crude oil exposure. Muscle acetylcholinesterase was not affected by oil exposure.     

Proteolytic activity associated with human erythrocyte membranes. Self-digestion of isolated human erythrocyte membranes.

At least two kinds of enzymes are active in the proteolytic self-digestion of erythrocyte membranes. The specific activities of these enzymes do not decrease with repeated washings of purified stroma. The effects of a variety of inhibitors on the membrane preparation's capacity to digest 125-I-labelled casein, covalently linked to latex beads, have been examined. Pepstatin-inhibitable enzyme, active at low pH, digests the membrane extensively to small polypeptide fragments. Spectrin, located at the internal part of the membrane, is readily degraded. Diisopropylfluorophosphate-inhibitable enzyme, active at pH 8-9, has only limited digestive capacity. Some of the membrane components, such as the small molecular weight glycoproteins, are resistant to digestion. The restricted capacity of digestion is due to the membrane molecular arrangement; increased disaggregation removes the restriction and increases the activity. Spectrin is not digested unless the membrane topography is disrupted by NP-40 neutral detergent. These observations suggest that the enzymes active at basic pH are located external to the cell. Intact cells do possess a limited capacity to degrade 125-I-labelled casein when their surfaces are brought into contact with substrate-coated beads.     

Forest responses to simulated elevated CO2 under alternate hypotheses of size‐ and age‐dependent mortality

Elevated atmospheric carbon dioxide (eCO₂) is predicted to increase growth rates of forest trees. The extent to which increased growth translates to changes in biomass is dependent on the turnover time of the carbon, and thus tree mortality rates. Size‐ or age‐dependent mortality combined with increased growth rates could result in either decreased carbon turnover from a speeding up of tree life cycles, or increased biomass from trees reaching larger sizes, respectively. However, most vegetation models currently lack any representation of size‐ or age‐dependent mortality and the effect of eCO₂ on changes in biomass and carbon turnover times is thus a major source of uncertainty in predictions of future vegetation dynamics. Using a reduced‐complexity form of the vegetation demographic model the Functionally Assembled Terrestrial Ecosystem Simulator to simulate an idealised tropical forest, we find increases in biomass despite reductions in carbon turnover time in both size‐ and age‐dependent mortality scenarios in response to a hypothetical eCO₂‐driven 25% increase in woody net primary productivity (wNPP). Carbon turnover times decreased by 9.6% in size‐dependent mortality scenarios due to a speeding up of tree life cycles, but also by 2.0% when mortality was age‐dependent, as larger crowns led to increased light competition. Increases in aboveground biomass (AGB) were much larger when mortality was age‐dependent (24.3%) compared with size‐dependent (13.4%) as trees reached larger sizes before death. In simulations with a constant background mortality rate, carbon turnover time decreased by 2.1% and AGB increased by 24.0%, however, absolute values of AGB and carbon turnover were higher than in either size‐ or age‐dependent mortality scenario. The extent to which AGB increases and carbon turnover decreases will thus depend on the mechanisms of large tree mortality: if increased size itself results in elevated mortality rates, then this could reduce by about half the increase in AGB relative to the increase in wNPP.