Linear density gradient separation of human lymphocyte subsets. II. Characterization of cells responding in secondary MLC and CML.

Lymphocytes were separated on linear density gradients (LDG) after they had been sensitized in vitro against allogeneic cells and had reverted to small cells. Cells from individual density fractions were restimulated with autologous, specific, or third-party cells and assayed 48 hr later for their response in secondary mixed leukocyte culture (MLC) and cell-mediated lympholysis (CML). Memory cells capable of responding in secondary MLC were broadly distributed and found in both heavy and light fractions. The various density classes of memory cells differed with respect to the degree of their specificity for the restimulating cells. In secondary MLC the greatest specificity for the originally sensitizing cells and the least cross-reactivity for third-party cells were primarily features of light- and medium-density cells. Memory killer cells for CML were fairly homogeneously grouped. Following restimulation, killers were enriched in light to medium fractions also, as was previously seen at the peak of the response on Day 6.     

Isolation of the globular region of the subcomponent q of the C1 component of complement.

Digestion after heat treatment of the subcomponent q of the C1 component of complement by collagenase leads to the isolation of the globular region of the protein. This product ('heads') is composed of three chains giving an overall molecular weight of about 57000. About half of the collagen-like region present in C1 q is lost after digestion. The 'heads' are shown to be soluble and hemolytically active products.     

Central projections of fibers in the auditory and tensor nerves of cicadas (Homoptera: Cicadidae)

Summary The auditory and tensor nerves of cicadas are mixed nerves containing both afferent and efferent elements. In 17-year cicadas, and in Okanagana rimosa, the auditory nerve contains afferents from body hairs, from the detensor tympani-chordotonal organ, and some 1300–1500 afferents from the hearing organ. Within the fused metathoracic-abdominal ganglionic complex the receptors from both the auditory and tensor nerves form a neuropilar structure that reveals the metameric organization of this complex. A few fibers run anteriorly, projecting into the meso and prothoracic ganglia. Within the ganglionic complex a division of auditory nerve afferents into a dense intermediate and a more diffuse ventral neuropile is observed. In addition, a dorsal motor neuropile is outlined by arborizations of the timbal motor neuron. This neuron is one of several efferent cell types associated with the auditory nerve, and there is an indication that several efferent fibers innervate the timbal muscle. There is anatomical evidence for a possible neuronal coupling between the bilaterally symmetrical large timbal motor neurons. In general, central projections from the auditory and tensor nerves support evidence of a structural layering within the CNS of insects.     

A high-activity ATP translocator in mesophyll chloroplasts of Digitaria sanguinalis, a plant having the C-4 dicarboxylic acid pathway of photosynthesis

The effect of exogenous adenine nucleotides on CO₂ fixation and oxygen evolution was studied with mesophyll protoplast extracts of the C₄ plant Digitaria sanguinalis. Exogenous ATP was found to stimulate the rate of pyruvate and pyruvate + oxalacetate induced CO₂ fixation, as well as reverse the inhibition of CO₂ fixation by carbonyl cyanide m-chlorophenyl hydrazone and several electron transport inhibitors. The ATP-dependent stimulation of CO₂ fixation varied from 40 to 70 μmol CO₂ fixed/mg chlorophyll per h, suggesting that ATP was crossing the chloroplast membranes at rates of 80–140 μmol/mg chlorophyll per h, since 2 ATP are required for each CO₂ fixed. Fixation of CO₂ could also be induced in the dark by exogenous ATP, in which case ADP accumulated outside the chloroplasts. This suggests that external ATP is exchanging for internal ADP. In contrast, ADP and AMP were found not to traverse chloroplast membranes, on the basis that neither nucleotide inhibited CO₂ fixation or stimulated oxygen evolution that was limited by available ADP for phosphorylation. Further evidence that ATP can enter the chloroplasts was obtained by direct measurements of the increase in ATP in the chloroplasts due to addition of exogenous ATP in the dark. These studies yielded minimal rates of ATP uptake on the order of 30–40 μmol/mg chlorophyll per h. It is suggested that a membrane translocator exists that specifically transports ATP into the chloroplasts in exchange for ADP. The significance of these findings are considered with respect to the C₄ pathway of photosynthesis.     

The action of beta-galactosidase (Escherichia coli) on allolactose.

The parameters involved in the action of beta-galactosidase (EC 3.2.1.23) (Escherichia coli) on allolactose, the natural inducer of lac operon in E. coli, were studied. At low allolactose concentrations only galactose and glucose were formed, while at high allolactose concentrations transgalactolytic oligosaccharides were also produced. Detectable amounts of lactose were not formed. The V and Km values (49.6 U/mg and 0.00120 M, respectively) indicated that allolactose is as good if not a better substrate of beta-galactosidase as lactose. The pH optimum with allolactose (7.8-7.9) as well as its activation by K+ (as compared to activation by Na+) were similar to the case with lactose as substrate. The alpha-anomer of allolactose was hydrolyzed about two times as rapidly as was the beta-anomer.     

The purification and study of a honey bee abdominal sucrase exhibiting unusual solubility and kinetic properties.

A sucrase from honey bee abdomens was purified to a high state of homogeneity. It was unusual in that it was completely soluble in high concentrations of ammonium sulfate and because curved rather than rectilinear lines were obtained when initial velocity data for at least two substrates were plotted. The action of the enzyme towards a large number of glycosides showed that the enzyme was able to hydrolyze all α-glucosides tested except trehalose and starch. pH Optima of sucrose and p-nitrophenyl-α-d-glucopyranoside differed by 1.0 pH unit. The unusual kinetic patterns which were found seem to be unique to this disaccharidase and were shown to be the result of a combination of hydrolytic and transferolytic activity in which the initial substrate is also a very good acceptor molecule for the transferolytic process. The K_m value for hydrolysis was found to be about an order of magnitude lower than for other insect sucrases with the more usual type of kinetic action. Amino acid and amino sugar analyses showed that the sucrase was a glycoprotein which contained glucosamine and either mannosamine or galactosamine. The molecular weight of the enzyme was estimated to be 70,000 or higher and there was no evidence that the enzyme had subunit structure. An s⁰_20,w value of 5.3S was determined. The enzyme was quite stable to a series of denaturing conditions and sulfhydryl reacting agents had little effect on the activity.