Aqueous channels are at the core of the translocase of the outer membrane (TOM) and the translocase of the inner membrane for the transport of preproteins (TIM23), the translocases mediating the transport of proteins across the outer and inner mitochondrial membranes. Yet, the existence of a channel associated to the translocase of the inner membrane for the insertion of multitopic protein (TIM22) complex has been arguable, as its function relates to the insertion of multispanning proteins into the inner membrane. For the first time, we report conditions for detecting a channel activity associated to the TIM22 translocase in organelle, i.e. intact mitoplasts. An internal signal peptide in the intermembrane space of mitochondria is a requisite to inducing this channel, which is otherwise silent. The channel showed slightly cationic and high conductance activity of 1000 pS with a predominant half-open substate. Despite their different composition, the channels of the three mitochondrial translocases were thus remarkably similar, in agreement with their common task as pores transiently trapping proteins en route to their final destination. The opening of the TIM22 channel was a step-up process depending on the signal peptide concentration. Interestingly, low membrane potentials kept the channel fully open, providing a threshold level of the peptide is present. Our results portray TIM22 as a dynamic channel solely active in the presence of its cargo proteins. In its fully open conformation, favored by the combined action of internal signal peptide and low membrane potential, the channel could embrace the in-transit protein. As insertion progressed and initial interaction with the signal peptide faded, the channel would close, sustaining its role as a shunt that places trapped proteins into the membrane.Most cells depend upon mitochondria to accomplish their programmed role. Along with mitochondria's own biogenesis, functioning and death entirely rely on protein translocation. The elevated protein content of mitochondria (ϳ700 different proteins in yeast (1)) and the four different compartments enclosed by their two membranes add to the complexity of protein trafficking pathways in this organelle. In addition, the need to maintain a low permeability of the inner membrane for coupling oxidative phosphorylation must be balanced with the passage of large molecules as proteins through water-filled channels. Focused on the route to their final destination inside mitochondria, three multisubunit complexes or translocases are depicted as the main machineries for specific recognition, import, and sorting of precursor proteins synthesized in the cytoplasm (for review, see Refs. 2-7).The translocase of the outer membrane (TOM) 3 is the common gate for the transport of every mitochondrial protein across the outer membrane (for review, see Ref. 8), and the TIM23 translocase imports matrix-targeted preproteins with cleavable amino-terminal presequences. Few proteins of the inner membrane (IM) containing a single transmembrane seg...
SHORT COMMUNICATIONS licles, and the total number of oocytes recovered, indicates that a major portion of oocytes were recovered from small follicles. This is in agreement with earlier studies in cattle in which the recovery of oocytes from large follicles was significantly lower compared with that from small and medium follicles (Pieterse and others 1991). In conclusion, this study demonstrates the feasibility of collecting oocytes by repeated oPu from clinically subfertile or infertile buffalo. Further studies are required to demonstrate that such buffaloes can be used as oocyte donors for long periods of time, and that the oocytes recovered can be used successfully for in vitro embryo production and the generation of viable offspring. Testicular and epididymal changes in rams following intoxication by Ferula communis
BECAUSE of the relatively small variation in the mature bodyweight of stallions and bulls, testicular size standards do not routinely relate to bodyweight. However, in dogs there may be a 10-fold variation in mature bodyweight and a high correlation between testicular weight and bodyweight has been shown (Woodall and Johnstone 1988a). Therefore, when evaluating if testicular size is normal for a dog, consideration must also be given to bodyweight, especially since one study found no differences between the weights of left and right canine testes (Zong-Han 1998). Therefore, the aim of this study was to gather and collect data concerning testicular weights, epididymal weights and bodyweights for the domestic dog (Canisfamiliaris).Twenty-nine adult intact male dogs of various breeds and of unknown health or breeding history were obtained from a local animal shelter after euthanasia. They were selected on the basis of their mature phenotype. Their canine teeth were examined, and only those with permanent canine teeth were included in the study. The scrotum of each dog was examined to ensure the presence of two scrotal testes. Each dog was weighed and the testes of each dog were removed. The epididymides were carefully dissected from the testes and the testes were then weighed separately on a balance, accurate to within 10 mg. All measurements were concluded within 10 minutes of testicular excision. Means (se) and coefficients ofvariation were calculated for each variable using standard procedures. Statistical comparisons were undertaken using the Student's t test.The dogs used in this study showed a 10-fold range in body mass, 5-5-fold range in testicular weight and 10-fold range in epididymal weight (Table 1). The mean (se) bodyweight was 15-4 (1.9) g. The mean weight of the right testes was 9*93 (0.9) g and weight of the left testes was 9 94 (1-0) g.The difference in weight between the right and left testes was not statistically significant. Similarly, there were no differences in weight between the right and the left epididymides (2-02 [0-2] g for both). The value for testes as a percentage of body mass was 0-13. A high correlation, however, was found between testicular weight and bodyweight (r=0-88); epididymal weight and bodyweight (r=0.80), and between epididymal weight and testicular weight (r=0-88). The statistical significance was P<0-001 for all the correlation coefficients.A functional relationship between the relative size of testes and requirements for sperm production has been demonstrated in a comparative survey of primate species (Harcourt and others 1981). It appears that testes are relatively large in primates and other mammals which have promiscuous mating systems where copulatory frequency is high and, where copulation is infrequent (monogamy system), the testes are small. Kenagy and Trombulak (1986) also indicated that a relationship between mating system and size of testes could possibly be generalised for some groups of mammals. The seven wild carnivores for which they obtained data (fox [Vulpe...
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