Characterization of zero-length cross-links between rabbit skeletal muscle troponin C and troponin I: evidence for direct interaction between the inhibitory region of troponin I and the NH2-terminal, regulatory domain of troponin C

Interactions between troponin C (TnC) and troponin I (TnI) play an important role in the Ca2(+)-dependent regulation of vertebrate striated muscle contraction. Previous attempts to elucidate the molecular details of TnC-TnI interactions, mainly involving chemically modified proteins or fragments thereof, have led to the widely accepted idea that the "inhibitory region" (residues 96-116) of TnI binds to an alpha-helical segment of TnC comprising residues 89-100 in the nonregulatory, COOH-terminal domain. In an attempt to identify other possible physiologically important interactions between these proteins, 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) was used to produce zero-length cross-links in the complex of rabbit skeletal muscle TnC and TnI. TnC was activated with EDC and N-hydroxysuccinimide (NHS) and then mixed with an equimolar amount of TnI [Grabarek, Z., & Gergely, J. (1988) Biophys. J. 53, 392a]. The resulting cross-linked TnCXI was cleaved with cyanogen bromide, trypsin, and Staphylococcus aureus V8 protease (SAP). Cross-linked peptides were purified by reverse-phase HPLC and characterized by sequence analysis. The results indicated that residues from the regulatory Ca2(+)-binding site II in the NH2-terminal domain of TnC (residues 46-78) formed cross-links with TnI segments spanning residues 92-167. The most highly cross-linked residues in TnI were Lys-105 and Lys-107, located in the inhibitory region. These results yield the first evidence for an interaction between the N-terminal domain of TnC and the inhibitory region of TnI.     

Location of SH-1 and SH-2 in the heavy chain segment of heavy meromyosin.

The two essential thiol groups of myosin, SH-1 and SH-2, have been localized in an ~ 20K segment of the heavy chain by analysis of the distribution of radioactivity after tryptic digestion of tryptic heavy meromyosin (HMM) or papain-HMM subfragment-1, both labeled at SH-1 and SH-2 with [¹⁴C]iodoacetamide and [¹⁴C]N-ethyl maleimide, respectively. The results are discussed in the framework of earlier work (Bálint, M., Sréter, F. A., Wolf, I., Nagy, B., and Gergely, J. (1975) J. Biol. Chem. 250, 6168–6177) on the tryptic fragmentation of myosin heavy chain and in the light of more recent work on the location of a fragment that reacts with a photoaffinity analog of ATP (Szilágyi, L., Bálint, M., Sréter, F. A., and Gergely, J. (1978) Fed. Proc. 37, 1695) and of suggestions concerning the binding of ATP in the region containing the SH-1 and SH-2 (Elzinga, M., and Collins, J. H. (1977) Proc. Nat. Acad. Sci. USA74, 4281–4284).     

Effect of cross-reinnervation on physiological parameters and on properties of myosin and sarcoplasmic reticulum of fast and slow muscles of the rabbit

Cross-reinnvervation of fast (extensor digitorum longus) and slow (soleus) twitch muscles of the rabbit showed essentially complete fast to slow and slow to fast conversion, respectively, 11-12 mo after surgery with respect to a number of physiological parameters including intrinsic shortening, velocity, and isometric twitch time to peak. There was pronounced bu incomplete biochemical conversion as judged by Ca2+ uptake by sarcoplasmic reticulum, myosin ATPase, alkali lability, and light chain complement. The question of trophic substances of neural origin is discussed in light of the fact that chronic stimulation for 15 wk of a fast muscle produces complete biochemical and physiological conversion to the slow type.     

Aurora-A-Dependent Control of TACC3 Influences the Rate of Mitotic Spindle Assembly

The essential mammalian gene TACC3 is frequently mutated and amplified in cancers and its fusion products exhibit oncogenic activity in glioblastomas. TACC3 functions in mitotic spindle assembly and chromosome segregation. In particular, phosphorylation on S558 by the mitotic kinase, Aurora-A, promotes spindle recruitment of TACC3 and triggers the formation of a complex with ch-TOG-clathrin that crosslinks and stabilises kinetochore microtubules. Here we map the Aurora-A-binding interface in TACC3 and show that TACC3 potently activates Aurora-A through a domain centered on F525. Vertebrate cells carrying homozygous F525A mutation in the endogenous TACC3 loci exhibit defects in TACC3 function, namely perturbed localization, reduced phosphorylation and weakened interaction with clathrin. The most striking feature of the F525A cells however is a marked shortening of mitosis, at least in part due to rapid spindle assembly. F525A cells do not exhibit chromosome missegregation, indicating that they undergo fast yet apparently faithful mitosis. By contrast, mutating the phosphorylation site S558 to alanine in TACC3 causes aneuploidy without a significant change in mitotic duration. Our work has therefore defined a regulatory role for the Aurora-A-TACC3 interaction beyond the act of phosphorylation at S558. We propose that the regulatory relationship between Aurora-A and TACC3 enables the transition from the microtubule-polymerase activity of TACC3-ch-TOG to the microtubule-crosslinking activity of TACC3-ch-TOG-clathrin complexes as mitosis progresses. Aurora-A-dependent control of TACC3 could determine the balance between these activities, thereby influencing not only spindle length and stability but also the speed of spindle formation with vital consequences for chromosome alignment and segregation.     

A new species of saw‐scaled viper of the Echis coloratus complex (Ophidia: Viperidae) from Oman,Eastern Arabia

A study of 353 museum specimens of the Echis coloratus complex from its entire range of distribution revealed an undescribed species in the United Arab Emirates and northern Oman. The results of UPGMA clustering and principal coordinate analysis of 138 male and 142 female specimens yielded for both sexes two major clusters, one with specimens from the UAE and northern Oman and one from southern and western Arabia, the Levant and Egypt. The new species has a longer tail with higher subcaudal counts; the lower prenasal scale is often missing and the upper prenasal is frequently fused with the nasal; the subnasal is often missing or fused with the nasal. The gular scales between the chin‐shield and the preventrals are round or only slightly elongate, not elongate as in Echis coloratus, and their number is higher. Other differences in characters of the gular area indicate a different scale structure of the ventral surface of the head. The new species is allopatric or parapatric with E. coloratus, but sympatric with Echis carinatus sochureki.     

Artificial Cardiac Pacemakers

Nine patients with complete heart block and Stokes-Adams disease were treated with subcutaneously implanted, fixed-rate, artificial cardiac pacemakers. All of these patients were refractory to medical treatment and confined to bed by the frequency of their attacks. One patient died in uremia one month after operation; in the remaining eight, the implanted pacemakers are providing adequate stimulation at present. These patients are free of seizures and show an improvement in the amount of their physical activity. A fixed rate of 60 to 65 per minute was adequate in all cases. The results of our clinical experience with cardiac pacemakers is satisfactory, but the possibility of mechanical failure limits their use to situations in which the patient is incapacitated despite medical treatment.     

Spruce sugars and poultry hydrolysate as growth medium in repeated fed-batch fermentation processes for production of yeast biomass

Bioprocess and Biosystems Engineering - The production of microbial protein in the form of yeast grown on lignocellulosic sugars and nitrogen-rich industrial residues is an attractive approach for...     

Scavenging behaviour and size-dependent carcass consumption of the black bullhead (Ameiurus melas)

This study examined the size-dependent scavenging behaviour of black bullheads Ameiurus melas under laboratory conditions, using common bleak Alburnus alburnus and pumpkinseed Lepomis gibbosus carcasses. Video camera observations showed that the activity of A. melas was higher at night, but substantial daytime activity was also recorded. Larger A. melas were more active than their smaller conspecifics, especially at night. All size classes exhibited a well-defined sequence of consuming different parts of the carcasses independent of size, but larger individuals tended to consume carcasses more efficiently. Carcasses of the softer-bodied A. alburnus were consumed more readily than those of the bonier L. gibbosus, independent of size. This scavenging behaviour of A. melas might facilitate the invasion success of the species.