O-acetylhomoserine sulfhydrylase (OAH SHLase) from Aspergillus nidulans is an oligomeric protein with a broad substrate specificity with regard to sulfhydryl compounds. As its Saccharomyces cerevisiae counterpart the enzyme also reacts with O-acetylserine and is inhibited by carbonyl reagents but not by antiserum raised against the yeast enzyme. In contrast to Saccharomyces cerevisiae the enzyme is not essential for Aspergillus nidulans as indicated by the completely prototrophic phenotype of OAH SHLase-negative mutants. Its major physiological role in Aspergillus nidulans seems to be recycling of the thiomethyl group of methylthio- adenosine but it is also a constituent of the alternative pathway of cysteine synthesis.
This work deals with the assessment of airway resistance in the course of a single breath. The study showed the presence of an early increase in the resistance at the beginning of expiration, which intensifies during expiration and ends up with a sharp decline during expiring the last remaining volume of ca 350 ml. The dynamic changes in airway resistance over a breath depend on the disharmonic interplay between diaphragm function and bronchial wall tonus. Thus, airway resistance is not constant during breathing, as could be misleadingly judged from the total resistance averaged over a breath. The study underscores the importance of recording the resistance-volume curves alongside the standard flow-volume curves to be able to discern the peculiarities of airway resistance changes during a single breath. Knowing changes in the instantaneous airway resistance characteristic for a given lung pathology could appreciably improve the diagnostic and therapeutic powers.