[Contribution to the knowledge of the biology of Cyclostomes: activity of aldolase in Lampetra planeri (Bloch) during its biological cycle]. / Contributo alla conoscenza della biologia dei Ciclostomi: attivita' aldolasica in Lampetra planeri (Bloch) durante il ciclo biologico.

It has been ascertained that in the Lampetra planeri (Bloch) the muscle and liver aldolase level in the last larval period in which lipids are accumulated strongly increases; this may be due to an increased synthesis or diminished degradation of the enzyme.

Role of tyrosine residues in cytoplasmic aspartate aminotransferase from beef kidney.

Cytoplasmic aspartate aminotransferase from beef kidney loses 25% of its activity on nitration with tetranitromethane while the apoenzyme about 95%. In the holoenzyme 0.5 tyrosine residue and 1.0 tyrosine residue in the apoenzyme are nitrated per enzyme protomer. In addition 1 cysteine residue per protomer is oxidized in both. The presence of substrates, alpha-ketoglutarate and glutamate, both at ten times their Km values, does not change these results. Mercaptoethanol does not affect the residual activity of either the nitrated holo or apoenzyme. Dithionite abolishes the activity of the nitrated holoenzyme by reducing tha coenzyme moiety. It has no effect on the native holoenzyme or on either the native or nitroapoenzyme.