The thiol groups of mouse immunoglobulin A. Incomplete formation of the C alpha 1-domain disulphide bridge.

The BALB/c IgA (immunoglobulin A) myeloma protein M167 contained on average 5.7 free SH groups per IgA dimer. These groups were preponderantly on the heavy chains and comprised two distinct populations: 3.3 exposed SH groups per dimer in the Fc region, and 2.4 buried SH groups per dimer in the Fd region, detectable o only after denaturation. To locate the cysteine residues involved, labelled peptides were purified from thermolysin digests of radioalkylated IgA by high-performance liquid chromatography. From the amino acid compositions of the peptides, the exposed thiol groups were assigned to Cys-307 in the C alpha 2 domain, which thus existed in the reduced form to an extent exceeding 80%. This residue may allow attachment of secretory component to dimer IgA in the mouse to proceed via thiol-disulphide exchange. The buried thiol groups were assigned to Cys-150 and Cys-208, in the C alpha 1 domain, each being in the reduced form to the extent of approx. 30%. This pair of residues would normally give rise to the characteristic intradomain disulphide bridge. It appears that disulphide formation is not a crucial event during folding of the C alpha 1 domain in IgA biosynthesis. The sequence in the region 140-151 was re-investigated, and residue 142 was shown to be serine, not cysteine, helping explain the lack of heavy-chain-light chain bonding in BALB/c mouse IgA. A disulphide-bond model for mouse IgA is proposed on the basis of these assignments and other features of the mouse alpha-chain sequence.     

Comparison of the structure of two cardiac troponin T isoforms.

Two isoforms of troponin T have been isolated from bovine cardiac muscle. One isoform has an Mr of 31000 and a pI at about 7.1, the corresponding values for the second isoform being 33000 and 6.5. Both isoforms have identical C- and N-terminal sequences, and, according to the data from tryptic-peptide mapping, a similar structure of the central and C-terminal domains. The large N-terminal peptides of troponin T isoforms differ in the content of glutamine/glutamic acid and alanine. It is concluded that the isoform with Mr 33000 has an additional peptide enriched with glutamic acid and alanine that is inserted between the N-terminal pentapeptide and the cysteine located 40-60 residues from the N-terminus.     

N2-(1-carboxyethyl)methionine. A ''pseudo-opine'' in octopine-type crown-gall tumours.

A novel methionine-containing plasmid-determined compound, N2-(1-carboxyethyl)methionine (NCEM) has been identified in crown-gall tumours induced by octopine-type strains of Agrobacterium tumefaciens. NCEM is probably synthesized by octopine synthase. Cell-free preparations from octopine-type strains of A. tumefaciens can degrade NCEM; however, the bacterium cannot transport the compound into the cell, although these strains can take up and degrade the octopine family of opines.     

Human glyceraldehyde-3-phosphate dehydrogenase: mRNA levels and enzyme activity in developing muscle.

Analysis of human glyceraldehyde-3-phosphate dehydrogenase mRNA revealed that levels in adult skeletal muscle are 12-fold greater per microgram of polyadenylated RNA than in fetal skeletal muscle, whereas in cardiac muscle RNA levels were about equal in fetal and adult tissue. The mRNA levels correlate well with glyceraldehyde 3-phosphate dehydrogenase enzyme activities. There was no evidence for fetus- or tissue-specific forms.     

Management of localized non-Hodgkin's lymphoma

Non-Hodgkin''s lymphomas (NHLs) are a heterogeneous group of disorders that vary widely in response to therapy. In Canada the modified Rappaport classification is used to categorize NHL. To facilitate the reporting and comparison of treatment results all cases should also be categorized in the terminology of the National Cancer Institute''s working formulation. The choice of therapy should be guided by specific prognostic factors: stage and bulk of the disease, patient''s age, presence of systemic symptoms and histologic subtype. Of these, the last appears to be the most important. Radiotherapy (RT) is the treatment of choice in localized low-grade lymphomas with favourable prognoses, while bimodal therapy (RT and chemotherapy [CT]) is warranted in presentations with unfavourable prognoses. Regional irradiation alone is indicated in intermediate-grade lymphomas with good prognoses (i.e., pathological stage I or II or clinical stage IA or IIA localized disease of small bulk in young patients). All other patients require CT followed by RT. The results of CT alone are encouraging but remain experimental. Aggressive therapy with multidrug regimens that include central nervous system prophylaxis is the foundation for successful treatment of high-grade NHL such as lymphoblastic lymphoma and diffuse small-noncleaved-cell lymphomas. Low-dose RT should be given to sites of bulky disease.     

Tissue abscission and wound healing in the operculum of Pomatoceros lamarckii Quatrefages (Polychaeta: Serpulidae)

Following opercular amputation in Pomatoceros lamarckii Quatrefages, wound healing is initiated from a predetermined point on the peduncle. The events of abscission, cell migration and cuticle deposition during wound healing have been studied by light and electron microscopy. Abscission occurs at a predetermined point on the peduncle indicated by specialized epidermal cells, the easy break-point cells (EBP). Following detachment of tissues distal to the EBP cells, the resultant wound is plugged by a knot of coelomocytes which provide a substratum over which epidermal cells migrate to seal and restore the epidermis. During their migration, the epidermal cells undergo differentiation and deposit a new cuticle. Cuticle formation is initiated by the deposition of a finely filamentous matrix. The fine filaments subsequently coalesce to form thicker fibrils which become aggregated into layers of orthogonally-arranged fibril bundles. The mechanisms involved in abscission, cell migration and cuticle deposition during wound healing of the opercular filament are discussed.     

Thermoregulation and metabolism in the smallest African gerbil, Gerbillus pusillus

The effect of temperature on thermoregulation, metabolism, evaporative water loss and thermal conductance was studied in Gerbillus pusillus . Its resting body temperature (TB) was 34·6°C, approximately 5°C higher than the mean ambient temperature (TA) encountered in its burrow. As TA increased above 34°C, its ability to lose heat to the environment decreased. It overcame this problem by tolerating increases in TB to a non-lethal maximum of 41°C, whilst also eliminating increasing quantities of obligate heat by pulmocutaneous evaporation and conduction.
Metabolic rate was 41% lower than that predicted from Kleiber's (1975) allometric equation. This confers a considerable saving in energy in an environment where food is often scarce, whilst simultaneously reducing heat production and the degree of gaseous exchange in the already oxygen-poor and carbon dioxide-rich environment encountered in the plugged burrows of its natural milieu.
Gerbillus pusillus , therefore, does not maintain strict homeothermy and utilizes a labile TB and reduced metabolic rate as an adaptive mechanism for survival in the arid zones of tropical Africa.     

Population fluctuations, reproduction and survival in the Striped fieldmouse Rhabdomys pumilio on the Cape Flats, South Africa

A wild population of Striped fieldmice was studied for a continuous period of five years in an area of alien Acacio bush about 24 km from Cape Town, South Africa. Mice were live-trapped, marked by toe-clipping and released on a 60-station grid, and also kill-trapped in a separate area. Marked annual fluctuations in the population size were correlated with a 6–8 month summer breeding season. There were also marked inter-annual differences in peak population size. The age of sexual maturity of females was determined from the first pregnancy which occurred at 6–7 weeks old; and of males from the presence of visible spermatozoa in the vas deferens which occurred at about 11 weeks old. Litter size was affected by both the age and the body mass of the female. It appeared that mean survival from birth was only approximately 1.5 months and that survival from first capture was about 1.9–2.5 months. This high mortality appeared to be the major reason for the sharp seasonal fluctuations in population size and may also have been responsible for the interannual differences since marked changes in survival were recorded between some years.