RESUMO
The effects of the Ca(2+)/H(+) exchanger A23187 and the K(+)/H(+) exchanger nigericin, the electrogenic membrane-potential depleters valinomycin and CCCP, and the calcium channel blockers ruthenium red, nifedipine, and nitrendipine on the apical growth of Phycomyces blakesleeanus were analyzed. While all of the compounds inhibited the growth of germlings in liquid medium, the Ca(2+) channel blockers were the least effective. Chitin synthesis in vivo was also sensitive to the inhibitors; here again, the calcium channel blockers were less efficient, and their effect occurred after a lag phase, in contrast to the electroneutral ionophores whose effects were immediate. The ionophores rapidly inhibited protein secretion, and reduced the number of secretory vesicles and chitosomes in the hyphal apex of P. blakesleeanus. The results suggest that not only tip-to-base calcium gradients but also transmembrane ionic gradients and membrane potential have a role in the apical growth of P. blakesleeanus. They are probably involved in the formation, migration, and/or fusion with the plasmalemma of secretory vesicles and chitosomes.
Assuntos
Bloqueadores dos Canais de Cálcio/farmacologia , Ionóforos/farmacologia , Phycomyces/efeitos dos fármacos , Phycomyces/crescimento & desenvolvimento , Calcimicina/farmacologia , Metabolismo dos Carboidratos , Carbonil Cianeto m-Clorofenil Hidrazona/farmacologia , Quitina/biossíntese , Hifas/efeitos dos fármacos , Hifas/ultraestrutura , Nifedipino/farmacologia , Nigericina/farmacologia , Nitrendipino/farmacologia , Phycomyces/metabolismo , Phycomyces/ultraestrutura , Transporte Proteico/efeitos dos fármacos , Rutênio Vermelho/farmacologia , Vesículas Secretórias/efeitos dos fármacos , Valinomicina/farmacologia , beta-Frutofuranosidase/metabolismoRESUMO
Addition of cycloheximide rapidly inhibited protein synthesis in Phycomyces blakesleeanus. In contrast, chitin biosynthesis decreased with biphasic kinetics displaying a slow and a rapid decay phases. Electron microscopic studies revealed a decrease in the number of apical vesicles and chitosomes after cycloheximide addition; and no change in wall thickness. It is proposed that the slow phase of decay in chitin biosynthesis represents the exhaustion of the pool of chitosomes which transport the chitin synthase necessary to maintain apical wall growth; whereas the second one corresponds to inactivation of the enzyme, which is short lived in vivo. Data also rule out a change in the polarization of wall synthesis induced by cycloheximide, as suggested in other systems.
Assuntos
Quitina/biossíntese , Cicloeximida/farmacologia , Vesículas Citoplasmáticas/efeitos dos fármacos , Phycomyces/efeitos dos fármacos , Antifúngicos/farmacologia , Parede Celular/efeitos dos fármacos , Parede Celular/ultraestrutura , Quitinases/antagonistas & inibidores , Quitinases/metabolismo , Vesículas Citoplasmáticas/ultraestrutura , Proteínas Fúngicas/análise , Proteínas Fúngicas/efeitos dos fármacos , Hifas/crescimento & desenvolvimento , Hifas/metabolismo , Hifas/ultraestrutura , Cinética , Phycomyces/citologia , Phycomyces/metabolismo , Phycomyces/ultraestrutura , Inibidores da Síntese de Proteínas/farmacologiaRESUMO
Diamino butanone (DAB), a competitive inhibitor of ornithine decarboxylase (ODC) a key enzyme in polyamine biosynthesis, inhibited the yeast to hyphae transition in Mucor rouxii, induced by transfer from anaerobiosis to aerobiosis, but not the opposite phenomenon. Addition of DAB to anaerobic yeast cells brought about a decrease in ODC and polyamine levels. In these conditions, the aerobic shift produced only a weak increase in ODC activity and no change in polyamine levels. DAB also blocked phorogenesis in M. rouxii and in Phycomyces blakesleeanus. At the effective concentrations DAB did not affect cell growth of either fungus. It is suggested that low, constant levels of ODC and polyamines are necessary for cell growth, and that high transient levels are required during the differentiative steps. DAB, at the concentrations used, affects this last process, but does not interfere with the maintenance level of polyamines.
Assuntos
Mucorales/efeitos dos fármacos , Putrescina/análogos & derivados , Diferenciação Celular/efeitos dos fármacos , Mucor/efeitos dos fármacos , Mucor/crescimento & desenvolvimento , Mucor/metabolismo , Mucorales/crescimento & desenvolvimento , Mucorales/metabolismo , Inibidores da Ornitina Descarboxilase , Phycomyces/efeitos dos fármacos , Phycomyces/crescimento & desenvolvimento , Phycomyces/metabolismo , Poliaminas/biossíntese , Putrescina/farmacologiaRESUMO
The presence of protein kinase C (PKC), a key enzyme in signal transduction, has not been investigated in fungal cells. The phorbol ester TPA, an activator of PKC, may be used as an indicator of the presence and role of PKC in Phycomyces blakesleeanus spores. Activation of spore germination by acetate was prevented by 6 nM TPA. The TPA analog 4 alpha PDD, an ineffective activator of PKC, did not affect spore germination. 3 mM dbcAMP, on the other hand, reversed the inhibition of germination caused by TPA. TPA-stimulated protein kinase activity was detected in spores. The possible relationship between PKC and the increased levels of cAMP that accompany the induction of spore germination is discussed.