Sedimentation Behaviour of Adenylsuccinase formed by Interallelic Complementation in Neurospora crassa

Adaptative features of ectothermic enzymes. III--Studies on phosphoglucose isomerase (PGI) from five species of tropical fishes of the superorder Ostariophysi

1. The electrokinetic and thermostability properties of phosphoglucose isomerase (PGI) in five species of tropical fish (Ostariophysi)-Leporinus friderici, L. silverstrii, Schizodon nasuttus, Hypostomus sp and Pimelodus maculatus--have been studied in order to study the adaptative nature of protein heterogeneity found in ectotherms. 2. Unlike most diploid fishes, the PGI of these species seemed to be encoded by three, four or five loci. 3. The subunits encoded by these loci occurred at different levels in the different tissues and organs analyzed. 4. Genetic variants at the three PGI loci were detected in two species of the family Anostomidae (L. friderici and S. nasuttus). In the family Pimelodidae, P. Maculatus showed a genetic variant as the Pgi-1 locus. 5. The product of these loci could be separated in three PGI regions based on their electrophoretic mobility, tissue distribution and thermostability properties. 6. The more anodal region (including isozymes and allozymes) was more thermolabile then the less anodal one, which is predominant in a single tissue-skeletal muscle.

Purification of argininosuccinase from Neurospora and comparison of some properties of the wild-type enzyme and an enzyme formed by inter-allelic complementation

Argininosuccinase has been purified from wild-typeNeurospora crassa, strain ST.A. The purified enzyme, which is homogeneous by the criteria of analytical centrifugation and starch-gel electrophoresis, has a molecular weight of about 175,000. The enzyme has also been partially purified from a heterokaryon between thearg-10 mutant stocks B317–9–9aand 402–3a.

The reaction kinetics of the two enzymes were compared in several respects, and they were found to be indistinguishable. The enzymes were also indistinguishable by starch-gel electrophoresis, and sedimented at the same rate through a sucrose gradient. It seems likely, however, that the enzymes do differ physically since they showed different affinities for both calcium phosphate gel and hydroxylapatite during purification.