Mixing patterns in Amazon lakes

The diel mixing patterns of two small floodplain lakes, Lago Jacaretinga in the Amazon drainage, and Lago Cristalino in the Rio Negro system, were investigated during both the high-water and low-water states of the Amazon River hydrograph. Measurements included temperature, oxygen, ammonia, phosphate, and chlorophyll. In both lakes thermal stratification developed during the day and was eroded at night. During the low-water period when the lakes were shallow, nocturnal circulation extended to the lake bottom, whereas when the lakes were deeper (greater than about 5 m), circulation did not reach the bottom and an anoxic hypolimnion developed. During the low-water period, percent of oxygen concentrations were relatively high but always less than saturation. Low oxygen concentrations were observed during the high-water period. At all times nocturnal mixing supplied a significant amount of oxygen to the lake ecosystems. Nighttime upward mixing of recycled nitrogen and phosphorus also appeared to be important nutrient sources for algal productivity.     

The plasminogen polymorphism in South African Negro populations: genetics and anthropogenetics

Summary Genetic polymorphism of human plasminogen (PLG) was investigated in 1252 unrelated individuals from eight South African Bantu-speaking Negro tribes. PLG phenotypes were determined by isoelectric focusing (pH 3.5–9.5 and 5–8 gradients) of neuraminidase-treated samples and subsequent detection by caseinolytic overlay or immunoblotting with specific antibody. No significant difference in the distribution of PLG alleles among the eight ethnic groups was observed. The combined allele frequencies of the common alleles in South African Negroes were 0.6977 for PLG*A, 0.2736 for PLG*B. In addition, six rare alleles were seen: PLG*A3, *A1, *M2, *B1, *B2, *B3. The rare variant PLG*B2 was proven to segregate by autosomal Mendelian inheritance in a family. The combined frequency for the rare alleles was 0.0287. The distribution of phenotypes in the total population sample was found to be in Hardy-Weinberg equilibrium. A striking difference in PLG allele distribution between Negroes from South Africa and published Negroid frequencies from North America could be observed. This difference was also seen in comparison with Mongoloid populations; in contrast, PLG frequencies for South African Negroes were similar or almost identical to known Caucasoid distributions.     

Standardization of Radiorenography in Dehydrated and Rehydrated Primates Under Laboratory Conditions

Radiorenography with ^99mTo-labelled diethylenctriaminepcntacetic acid ([^99mTc]-DTPA) was performed on chacma baboons (Papio ursinus) and vervet monkeys (Cereopithecus pygerythus) to establish the effects of various states of hydration on the data obtained from the DTPA-renogram. The renogram parameters, which can be related to certain aspects of kidney function, varied significantly with the degree of hydration. It is therefore imperative for clinically directed animal research projects on the urinary system to standardise the experimental procedure for radiorenography. A dehydration of 6 h followed by an hour IU rehydration period using 200 ml of a 0.9% NaCI solution on baboons under thiopentone sodium anaesthetic, was found to be the most suitable procedure for radiorenographic investigations in this primate model.     

Fluorescence polarization as a tool to study lectin-sugar interaction

The binding ofRicinus communis agglutinin andAbrus agglutinin to 4-methylumbelliferyl β-D-galactopyranoside was studied by equilibrium dialysis, fluo-rescence quenching and fluorescence polarization. The number of binding sites and the association constant value obtained by fluorescence polarization for bothRicinus communis agglutinin andAbrus agglutinin are in close agreement with those obtained by the other methods. This indicates the potential of ligand-fluorescence polarization measurements in the investigation of lectin-sugar interactions.     

Lectins from<Emphasis Type="Italic">Griffonia simplicifolia</Emphasis> seeds

The physical-chemical and carbohydrate binding specificity ofGriffonia simplicifolia I (GS I) isolectins, one of the 4 lectins isolated fromGriffonia simplicifolia seeds, are described.Association constants for the binding of methyl α- and β-D-galactopyranoside and methyl 2-acetamido-2-deoxy-α-D-galactopyranoside to the A₄, A₂ B₂ and B₄ isolectins are reported.Precipitation reactions of theGriffonia simplicifolia isolectins with guaran and type B blood group substance are described.The hypothesis that subunit B is a precursor of subunit A, a process involving proteolytic cleavage of the B subunit, was tested by conducting structural studies on the 2 subunits. The results indicated that the A and B subunits are probably products of 2 separate but closely related, possibly contiguous genes.     

Haemolysis of rabbit erythrocytes by a lectin from the seeds of<Emphasis Type="Italic">Croton tiglium</Emphasis>

The kinetics of haemolysis of rabbit erythrocytes byCroton tiglium lectin was studied as a function of concentration of the lectin and erythrocytes. The length of the prelytic period decreased with increasing lectin concentrations, indicating that the secondary events at the membrane which follow the binding of the lectin to cell surface carbohydrate receptors are accelerated at higher surface concentrations of the lectin. The rate or extent of haemolysis was not affected by the inclusion of ions like K⁺, Ca²⁺ and Mg²⁺ in the medium or by the substitution of ionic medium by a non-ionic medium. The inhibition of haemagglutination and haemolysis of rabbit red cells byCroton tiglium lectin by antilectin rabbit serum was observed. A possible mechanism of haemolysis by the lectin is discussed.     

Plant lectins specific for N-acetyl-β-D-galactosamine

N-Acetyl-D-galactosamine in β-linkage being ubiquitous in cell surface glycoproteins, their interaction with lectins specific for this sugar moiety may be a significant event in cell adhesion phenomena. This article discusses the common β-N-acetyl galactosamine-specific lectins, with particular stress on the lectin from winged beans (Psophocarpus tetragonolobus).     

Role of Peroxidase when Hydroxyproline-rich Protein in Plant Cell Walls is increased by Ethylene

Ethylene may control the growth of plant cells by regulating hydroxylation of specific wall proteins.     

Genetic Control of Variable and Constant Regions of Immunoglobulin Heavy Chains

IMMUNOGLOBULIN polypeptide chains consist of two well defined regions designated the “variable region” and the “constant region”. Whereas great diversity exists in amino-acid sequences of variable regions, the constant regions of a given subclass of heavy chains (C_H)^* are essentially invariant in sequence^{1, 2}. Exceptions are the allelic forms, such as the rabbit allotypes A14 and A15^{3, 4}, where a threonine-alanine interchange occurs in the constant region of γ chains (Appella, Chersi, R. G. M. and Dubiski, in preparation). The markers unique to a chains (for example, A14-A15) are closely linked to allotypic markers at the a locus (a1, a2, a3)^{3, 4} which seem to be present on four different Ig heavy chain classes (α, γ, ε, µ)^5–7. These puzzling observations can be explained if the a locus determinants are variable region markers which reflect genetically controlled differences in some relatively constant residues within the V_H region sequences⁷.