Long term stability of lysine vasopressin and of specifically tritiated lysine vasopressin in weakly acidic aqueous solutions

Lysine vasopressin tritiated at meta position of tyrosine (1.9 Ci/mmole) decomposes during a long storage period, mainly as a result of radiolysis. The loss of specific activity by isotopic exchange with water is slow. The nonlabelled peptide undergoes only very minute decomposition (polymerization). Specific radioactivity declines with a half life of 47.4 months.

alpha-Actinin promotes polymerization of actin from profilactin

The effect of alpha-actinin on profilactin has been analyzed. The results show that addition of submolar ratios of alpha-actinin to a profilactin sample leads to a dissociation by the profilin-actin complex and polymerization of actin. The newly formed filaments are cross-linked by alpha-actinin.

Reorganization of actin in platelets stimulated by thrombin as measured by the DNase I inhibition assay

The effect of thrombin stimulation on actin organization in human platelets has been analyzed by using the DNase I inhibition assay, which is selective for unpolymerized and filamentous actin. The results provide biochemical evidence for the suggestion that stimulation leads to rapid polymerization of actin. The measurements also reveal changes in the polymerization state of actin occurring after cell lysis. These changes are influenced by the concentration of free calcium in the extracts.

Selective assay of monomeric and filamentous actin in cell extracts, using inhibition of deoxyribonuclease I

A simple and selective assay for monomeric and filamentous actin is presented, based on the inhibition of DNAase I by actin. In mixtures of monomeric and filamentous actin, only the monomeric form is measured as DNAase inhibitor. The total amount of actin in a sample can be determined after depolymerization of F actin with guanidine hydrochloride. The assay is rapid enough to detect changes in the polymerization state of actin in vitro over time intervals as short as 3 min. Data characterizing unpolymerized and filamentous actin pools in extracts of human platelets, lymphocytes and HeLa cells are presented.

Prolonged serum insulin decreasing effects of two synthetic somatostatin analogues studied in vivo by a new animal method. Preliminary communication

A newly developed in vivo method, using the ob-ob strain of obese-hyperglycaemic mice with permanently very high serum insulin values, makes it possible to detect more prolonged serum insulin lowering properties than in normal animals. Two newly synthesized analogues of somatostatin, D-alanine-somatostatin and des-alanine-des glycine-des-amino-somatostatin produced a more prolonged and greater decrease in the serum insulin values of ob-ob mice than did somatostatin. Our new in vivo method makes it possible to investigate the duration of insulin suppression of new derivatives.

Anti-actin specificity of human smooth muscle antibodies in chronic active hepatitis

Thirty sera reacting by IFL technique in titres greater than or equal to 100 with smooth muscle fibres of rat stomach, rat renal glomeruli, and with the membrane region of thyroid cells were randomly chosen among sera sent in for routine testing of tissue antibodies. All sera but one were found to be derived from patients with chronic active hepatitis. The smooth muscle and other relevant cell staining were abolished after absorption of sera with actin, prepared from rabbit skeletal muscle and found to be homogeneous by SDS gel-electrophoresis and by electron microscopy. The actin anti-bodies were purified by precipitation of sera with F-actin and elution of the precipitates at acid pH. The purified antibodies stained all tissues in the same way as the original sera. In double immunodiffusion tests all thirty sera gave precipitation with actin. Thus, it was concluded that these broad-reacting SMA are directed against actin. The finding of high-titred SMA is of diagnostic value and supports the clinical diagnosis of active chronic hepatitis. In addition, anti-actin antibodies eluted from human sera are a suitable tool for studying actin-containing cellular structures.