Search

Specific contributions of tyrosyl and of tryptophanyl residues can be distinguished in the near-ultraviolet circular dichroic spectrum of staphylococcal nuclease. Upon binding of the inhibitor deoxythymidine 3',5'-diphosphate in the presence of Ca(++), a significant change in the circular dichroic spectrum results which has been used to characterize the interaction of ligand and enzyme. The data suggest that the asymmetric environment of certain tyrosyl residues is altered by binding of the nucleotide inhibitor.

Suspensions of Staphylococcus aureus Foggi strain were exposed to nitrosoguanidine and screened on deoxyribonucleic acid-acridine orange-agar plates for loss of extracellular nuclease activity. All nuclease-deficient mutants lacked cross-reacting material when tested with antinuclease antibody. Coagulase and beta-hemolysin were also lost in nuclease-deficient mutants, and all three enzyme functions were regained together upon reversion with ethyl methane sulfonate. These observations are consistent with the suggestion that the synthesis or the release, or both the synthesis and release, of certain extracellular enzymes may be subject to coordinated control mechanisms.

Ectopic production of polypeptide hormones by tumors of nonendocrine tissues can serve as a clue to diagnosis of the tumor and as a focus for management of the patient with cancer. In the differential diagnosis of syndromes of endocrine hyperfunction, the ectopic hormone syndromes have achieved an increasingly prominent position. Available evidence on the properties of ectopic ACTH, MSH, parathyroid hormone, erythropoietin, gonadotropins, and thyrotropin is consistent with the unifying hypothesis of genetic derepression.