Inhibitory and stimulatory action of vasopressin on the secretion of corticotrophin in rats : structure-activity study

The effect of intracerebroventricular injection of graded amounts of vasopressin and related peptides on plasma ACTH levels was investigated. Picogram amounts of vasopressin and oxytocin suppressed ACTH levels whereas nanogram amounts of vasopressin resulted in a pronounced increase in plasma ACTH levels. The time course of this stimulatory action was found to be different to that of the inhibitory action. The desglycinamide analogue of vasopressin was less potent in suppressing ACTH release and the C-terminal tripeptide did not affect plasma ACTH levels. However, the C-terminal tripeptide of oxytocin suppressed ACTH release while the desglycinamide analogue was ineffective. Vasotocin and its desglycinamide analogue appeared to be equipotent, although both were less active than vasopressin and oxytocin in this respect. We conclude that the entire vasopressin molecule is needed to suppress ACTH release while oxytocin may exert its inhibitory action through a smaller fragment of the molecule.     

The stability of the lactose and citrate plasmids in Lactococcus lactis subsp. lactis biovar. diacetylactis

We have studied the intraperoxisomal location of catalase in peroxisomes of methanol-grown Hansenula polymorpha by (immuno)cytochemical means. In completely crystalline peroxisomes, in which the crystalline matrix is composed of octameric alcohol oxidase (AO) molecules, most of the catalase protein is located in a narrow zone between the crystalloid and the peroxisomal membrane. In non-crystalline organelles the enzyme was present throughout the peroxisomal matrix. Other peroxisomal matrix enzymes studied for comparison, namely dihydroxyacetone synthase, amine oxidase and malate synthase, all were present throughout the AO crystalloid. The advantage of location of catalase at the edges of the AO crystalloids for growth of the organism on methanol is discussed.