T-cell responsiveness in Mycobacterium lepraemurium infections in a "resistant" (CBA) and a "susceptible" (BALB/c) mouse strain

Antigen-specific and mitogen-nonspecific T-lymphocyte proliferation and lymphokine release (interleukin 2 and macrophage activation factor) were studied in BALB/c and CBA mice infected intravenously with 10(8) Mycobacterium lepraemurium organisms. The responsiveness of spleen cells from infected animals to Con A and specific MLM antigen declined as the infection progressed. Thus, the decreased responsiveness appeared earlier and was more profound in the relatively susceptible BALB/c strain than in the relatively resistant CBA strain. Nylon-wool-purified, T-cell-enriched spleen cells from both strains, however, responded to both M. lepraemurium antigen and Con A until the later stages of infection (17 weeks postinfection). The relevance of nonspecific immunodepression mediated by nylon-wool-adherent spleen cells to the progressive nature of this infection is discussed.     

Partial deficiency of hypoxanthine-guanine phosphoribosyltransferase with reduced affinity for PP-ribose-P in four related males with gout

Summary A family is described in which four affected males, spanning two generations, have hyperuricemia and gout accompanied by hematuria but are without severe neurologic involvement. The affected males were found to have markedly reduced levels of erythrocytic hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity; these were 5–12% with hypoxanthine and 0.5–3% with guanine as compared to controls. Erythrocytic adenine phosphoribosyltransferase (APRT) was approximately three-fold elevated in the affected individuals.The residual HGPRT activity in affected males enabled characterization of some of the properties of this mutation. The apparent Michaelis constants (km) for both hypoxanthine and guanine were essentially unchanged, whereas the km for PP-ribose-P was approximately 10–20-fold elevated for all four affected males. The enzyme was more sensitive to product inhibition by IMP and GMP than controls, and exhibited greater thermal lability at 65°C than found with control lysates.     

Evidence for regulation of actin synthesis in cytochalasin D-treated HEp-2 cells

In HEp-2 cells treated with 0.2 or 2.0 μM cytochalasin D (CD), the relative rate of actin synthesis increased for about 12 h and then reached a plateau; this increase was suppressed by actinomycin D (AD). When CD was washed from cells which had been treated for 20 h, the elevated rate of actin synthesis declined to the control value within ca 4 h, as the actin-containing cytoskeletal components rearranged by CD recovered their normal morphology. Subsequently, actin synthesis was depressed below control values for a prolonged period; during recovery from 2 h treatment with CD, this depression was of much shorter duration. Re-addition of CD to cells after a 3 h recovery period again induced the cytoskeletal alterations characteristic of CD treatment but did not reverse the prior decline in the rate of actin synthesis. In HEp-2 cells treated with cycloheximide during exposure to CD for 20 h, the relative rate of actin synthesis measured after removal of cycloheximide was twofold higher than with CD alone and such cells exhibited a twofold slower decline in the rate of actin synthesis during recovery from CD in the continued presence of cycloheximide. These effects of cycloheximide, which resemble observations on “super-induction”, suggest that actin synthesis in CD-treated and recovering HEp-2 cells may be regulated by a repressor protein. The possibility that the proposed repressor protein is actin and that actin may thus be a feedback inhibitor of its own synthesis is discussed.     

Thermal sensitivity of scope for activity in Pagothenia borchgrevinki, a cryopelagic Antarctic nototheniid fish

The thermal sensitivity of scope for activity was studied in the Antarctic nototheniid fish Pagothenia borchgrevinki. The scope for activity of P. borchgrevinki at 0°C was 189 mg O₂ kg⁻¹ h⁻¹ (factorial scope 6.8) which is similar to that of temperate and tropical species at their environmental temperatures, providing no evidence for metabolic cold adaptation of maximum activity. The scope for activity increased to a maximum value of 266 mg O₂ kg⁻¹ h⁻¹ (factorial scope 8.3) at 3°C and then decreased from 3 to 6°C. The thermal sensitivity of critical swimming speed was also investigated and followed a similar pattern to aerobic scope for activity, suggesting oxygen limitation of aerobic performance. Oxygen consumption rates and ventilation frequencies were monitored for 24 h after the swimming challenge and the recovery of both parameters to resting levels was rapid and independent of temperature.     

The catalytic site residues and interfacial binding of human pancreatic lipase.

In this study, the essential serine residue and 2 other amino acids in human pancreatic triglyceride lipase (triacylglycerol acylhydrolase, EC 3.1.1.3) were tested for their contribution to the enzyme's catalytic site or interfacial binding site. By site-specific mutagenesis of the cDNA for human pancreatic lipase, amino acid substitutions were made at Ser153, His264, and Asp177. The mutant cDNAs were expressed in transfected COS-1 cells. Both the medium and the cells were examined for the presence of pancreatic lipase by Western blot analysis. The activity of the expressed proteins against triolein and the interfacial binding was measured. Proteins with mutations in Ser153 were secreted by the cells and bound to interfaces but had no detectable activity. Changing His264 to a leucine or Asp177 to an asparagine also produced inactive lipase. Substituting glutamic acid for Asp177 produced an active protein. These results demonstrate that Ser153 is involved in the catalytic site of pancreatic lipase and is not crucial for interfacial binding. Moreover, the essential roles of His264 and Asp177 in catalysis were demonstrated. A Ser-His-Asp catalytic triad similar to that present in serine proteases is present in human pancreatic lipase.