The carbon cycle and carbon dioxide over Phanerozoic time: the role of land plants

A model (GEOCARB) of the long-term, or multimillion year, carbon cycle has been constructed which includes quantitative treatment of (1) uptake of atmospheric CO₂ by the weathering of silicate and carbonate rocks on the continents, and the deposition of carbonate minerals and organic matter in oceanic sediments; and (2) the release of CO₂ to the atmosphere via the weathering of kerogen in sedimentary rocks and degassing resulting from the volcanic-metamorphic-diagenetic breakdown of carbonates and organic matter at depth. Sensitivity analysis indicates that an important factor affecting CO₂ was the rise of vascular plants in the Palaeozoic. A large Devonian drop in CO₂ was brought about primarily by the acceleration of weathering of silicate rock by the development of deeply rooted plants in well-drained upland soils. The quantitative effect of this accelerated weathering has been crudely estimated by present-day field studies where all factors affecting weathering, other than the presence or absence of vascular plants, have been held relatively constant. An important additional factor, bringing about a further CO₂ drop into the Carboniferous and Permian, was enhanced burial of organic matter in sediments, due probably to the production of microbially resistant plant remains (e.g. lignin). Phanerozoic palaeolevels of atmospheric CO₂ calculated from the GEOCARB model generally agree with independent estimates based on measurements of the carbon isotopic composition of palaeosols and the stomatal index for fossil plants. Correlation of CO₂ levels with estimates of palaeoclimate suggests that the atmospheric greenhouse effect has been a major factor in controlling global climate over the past 600 million years.     

Aerobic power and anthropometric characteristics of Hungarian schoolboys

A sample of 989 male youngsters aged 11–18 years was subdivided into three groups by the type and amount of their physical activity as follows. Group 1 (G1) had a maximum of three curricular PE classes a week, without any additional organized physical activity. With the same number of PE lessons Group 2 (G2) had at most three sessions of sports training per week in addition. Group 3 (G3) had a weekly minimum of five training sessions in addition to the PE lessons at school. The subjects of G3 had significantly higher relative aerobic power, larger relative muscle mass and smaller relative body fat content than the subjects of the other two groups. The effects of sports training on the development of physical working capacity are undeniable, but to explain such differences observed in relative aerobic power between the groups requires also the consideration of inheritance and selection procedure.     

A century of pathology at Yale: personal reflections.

This history is largely about the players on the stage of the Yale Pathology Department acting out their roles as observed by the author in over a half century as a member of the department and as associate dean of the medical school.     

Intracellular proteolysis: Signals of selective protein degradation

Selective proteolysis is one of the mechanisms for the maintenance of cell homeostasis via rapid degradation of defective polypeptides and certain short-lived regulatory proteins. In prokaryotic cells, high-molecular-mass oligomeric ATP-dependent proteases are responsible for selective protein degradation. In eukaryotes, most polypeptides are attacked by the multicatalytic 26S proteasome, and the degradation of the majority of substrates involves their preliminary modification with the protein ubiquitin. The proteins undergoing the selective proteolysis often contain specific degradation signals necessary for their recognition by the corresponding proteases. This article is dedicated to the 25th Anniversary of the journal Bioorganicheskaya Khimiya     

Microbial production of d-amino acids

The production of d-aminoacylase by Alcaligenes denitrificans and Alcaligenes faecalis has been studied. The enzyme was inducibly produced and N-acetyl-d-leucine and N-acetyl-d-valine were the most effective inducers. d-methionine, d-valine, d-phenylalamine and d-leucine were produced by the enzymic hydrolysis of the appropriate N-acetyl-d-amino-acids with whole cell biomass. The hydrolysis of N-acetyl-d-methionine by A. denitrificans and N-acetyl-d-valine by A. faecalis was preferential. Maximum yields of d-methionine and d-valine were 94.3 and 84.7% at a specific product formation rate of 20.10 and 19.19 μmol min⁻¹ mg⁻¹ of wet cells at 20 mM substrate concentration and 5 mg ml⁻¹ of cell density.     

Evolution of the Cholecystokinin and Gastrin Peptides and Receptors

The intestinal hormone, cholecystokinin (CCK), and the stomachhormone, gastrin, form a simple two member family of peptideswith much to offer students of hormone and receptor evolution.They share a common carboxyl-terminal tetrapeptide sequence,which is the bioactive site of each peptide and is also antigenic,making heterologous biological and immunological assays feasible.Current evidence indicates that CCK evolved in chordate ancestorsand that gastrin-like peptides that separately regulate stomachfunctions evolved from an ancestral CCK at the level of thedivergence of tetrapods from fish. This tentative conclusionmay require modification when the two separate CCK- and gastrin-likepeptides recently identified in the dogfish shark are characterizedfurther. The CCK-X receptor appears to be ancestral to the CCK-Aand CCK-B receptors identified in amniotes. The evolution ofgastrin and of CCK-A and -B receptors may have played rolesin the evolution of the stomach and the evolution of endothermyin vertebrate phylogeny.     

Mechanical effects of pharyngeal constrictor activation on pharyngeal airway function

The mechanicaleffects of pharyngeal constrictor (PC) muscle activation on pharyngealairway function were determined in 20 decerebrate, tracheotomized cats.In 10 cats, a high-compliance balloon attached to a pressure transducerwas partially inflated to just occlude the pharyngeal airway. Duringprogressive hyperoxic hypercapnia, changes in pharyngeal balloonpressure were directly related to phasic expiratory hyopharyngeus(middle PC) activity. In two separate protocols in 10 additional cats,the following measurements were obtained with and without bilateralelectrical stimulation (0.2-ms duration, threshold voltage) of thedistal cut end of the vagus nerve's pharyngeal branch supplying PCmotor output: 1) pressure-volumerelationships in an isolated, sealed upper airway at a stimulationfrequency of 30 Hz and 2) rostrally directed axial force over a stimulation frequency range of 0-40 Hz. Airway compliance determined from the pressure-volume relationships decreased with PC stimulation at and below resting airway volume. Compared with the unstimulated condition, PC stimulation increased airway pressure at airway volumes at and above resting volume. Thisconstrictor effect progressively diminished as airway volume wasbrought below resting volume. At relatively low airway volumes belowresting volume, PC stimulation decreased airway pressure compared withthat without stimulation. PC stimulation generated a rostrally directedaxial force that was directly related to stimulation frequency. Theresults indicate that PC activation stiffens the pharyngeal airway,exerting both radial and axial effects. The radial effects aredependent on airway volume: constriction of the airway at relativelyhigh airway volumes, and dilation of the airway at relatively lowairway volumes. The results imply that, under certain conditions, PCmuscle activation may promote pharyngeal airway patency.

     

Functional changes in the structure of the SRP GTPase on binding GDP and Mg2+GDP.

Ffh is a component of a bacterial ribonucleoprotein complex homologous to the signal recognition particle (SRP) of eukaryotes. It comprises three domains that mediate both binding to the hydrophobic signal sequence of the nascent polypeptide and the GTP-dependent interaction of Ffh with a structurally homologous GTPase of the SRP receptor. The X-ray structures of the two-domain 'NG' GTPase of Ffh in complex with Mg2+GDP and GDP have been determined at 2.0 A resolution. The structures explain the low nucleotide affinity of Ffh and locate two regions of structural mobility at opposite sides of the nucleotide-binding site. One of these regions includes highly conserved sequence motifs that presumably contribute to the structural trigger signaling the GTP-bound state. The other includes the highly conserved interface between the N and G domains, and supports the hypothesis that the N domain regulates or signals the nucleotide occupancy of the G domain.