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M A Hanson

Publications and source records attributed to M A Hanson.

156 records · Page 9Linked to original sources
PubMed1975

Control of the synthesis of a single enzyme by multiple regulatory circuits in Neurospora crassa.

Neurospora crassa synthesizes and secretes an extracellular protease into its growth medium when an exogenous protein serves as its principal source of sulfur, nitrogen, or carbon. The enzymes produced under these three growth conditions have been compared by a number of criteria. The results indicate that the same extracellular protease with a molecular weight of 31,000 is synthesized during the three different metabolic conditions. A regulatory mutant, which lacks a positive signal required for the synthesis of a family of related enzymes for sulfur metabolism, cannot synthesize the protease in response to a limitation for sulfur; yet, this same mutant is capable of producing the enzyme when it is limited for either nitrogen or carbon. A second regulatory mutant, defective in the control of nitrogen metabolism, fails to synthesize the protease only when it is limited for nitrogen. The evidence suggests that a single structural gene for this extracellular protease exists and that it is regulated in a complex fashion such that control signals arising from any one of the three distinct regulatory circuits can activate it for expression. A model is proposed for complex regulation of the synthesis of this enzyme.

Cycloheximide↗
PubMed1973

Regulation of a sulfur-controlled protease in Neurospora crassa.

Wild-type Neurospora crassa produces and secretes extracellular protease(s) when grown on a medium containing a protein as its principle sulfur source. Readily available sulfur sources, such as sulfate or methionine, repress the synthesis of the proteolytic activity. Preliminary characterization of the proteolytic enzyme shows it to have a molecular weight of about 31,000, a pH optimum of 6 to 9 with casein as substrate, and esterolytic activity against acetyl-tyrosine ethyl ester with a pH optimum of 8.5. The enzyme activity is completely inhibited by diisopropylfluorophosphate, partially inhibited by ethylenediaminetetraacetate, but unaffected by iodoacetate. The proteolytic activity is temperature labile and is reduced by 75% within 15 min at 60 C. Synthesis of the protease activity is induced by proteins, and to a lesser extent by large-molecular-weight polyamino acids, but not at all by small peptides or amino acid mixtures. During conidial out-growth, the protease(s) first appears at about 8 h and continues to increase while the cells are in an active growth phase. When a low concentration of sulfate is present, the protease(s) is not produced until about 18 h, suggesting that the sulfate must first be used by the cells before the protease is either synthesized or released.

Chromatography, Gel↗
PubMedDate not supplied

Visualisation and measurement of tracheal diameter in the sheep fetus: an ultrasound study with stereomicroscopic correlation.

OBJECTIVE: There is no information on ultrasonographic visualisation of the upper airways in the sheep fetus, but this species permits to examine the accuracy of ultrasonography in measuring the inner tracheal diameter. This was the aim of our study. METHODS: Transabdominal ultrasonography to visualise the trachea was attempted in 16 unsedated Welsh Mountain ewes with a singleton pregnancy at 70 (SD 2) days gestation (term 148 days). The ultrasonographically measured inner tracheal diameter was compared with the actual inner tracheal diameter obtained by stereomicroscopy post-mortem. RESULTS: High-resolution ultrasonography permitted clear imaging of the fetal trachea in 87% (14/16) of the cases analysed. The ultrasound measurements were smaller than the corresponding stereomicroscopic measurements, the mean +/- SD difference between the measurements being 0.40 +/- 0.12 mm. CONCLUSIONS: Improvements in ultrasound have led to increased interest in the assessment of the trachea in human fetuses. Our study in the ovine fetus at mid gestation shows that optimal views of the fetal trachea allowing accurate measurements can be obtained in almost all the cases.

Animals↗