Succinyl-trialanine p-nitroanilide (Suc-Ala3-pNA), a synthetic substrate for the determination of elastase activity, was hydrolyzed in sequence by two enzymes that were found to be associated with human high-density lipoproteins. The enzymes involved in the sequence of reaction were separated by ion-exchange chromatography from apo-lipoprotein A-I and A-II, major apoproteins of high-density lipoproteins. One, designated as fraction MK, cleaves Suc-Ala3-pNA to succinyl-dialanine and alanine p-nitroanilide (Ala-pNA), and the other, designated as fraction U, cleaves Ala-pNA to alanine and p-nitroaniline. Fraction MK was inhibited by dithiothreitol, EDTA, and 1,10-phenanthroline, whereas fraction U was inhibited by 1,10-phenanthroline and bestatin. In addition to these findings, fraction MK also hydrolyzed 2,4-dinitrophenyl-prolyl-glutaminyl-glycyl-isoleucyl-alanyl-glycyl-glutaminyl- arginine (DNP-octapeptide), a specific substrate for the determination of vertebrate collagenase. Neither native elastin nor native collagen was hydrolyzed by a mixture of the two enzymes. Fraction U was very similar to aminopeptidase M with respect to its enzyme characteristics studied.

Humans↗

PubMed1983

Effect of glucocorticoids on alpha-2 adrenoceptors in vas deferens of reserpinized rat in organ culture.

The changes in alpha adrenoceptors in vasa deferentia of reserpinized rats in organ culture were examined by binding studies with 3H-clonidine, 3H-yohimbine and 3H-prazosin. On organ culture for 1 day, the 3H-clonidine binding sites decreased by 1.07 pmol/g tissue and after 2 days no binding sites were detectable. 3H-Yohimbine binding sites also decreased during culture, but in smaller extent than 3H-clonidine binding sites. On the other hand, 3H-prazosin binding sites showed no apparent change in amount during culture. Addition of 0.1 mM hydrocortisone or dexamethasone to the culture medium inhibited the decrease in 3H-clonidine binding sites (1.7 pmol/g tissue), and the effect of glucocorticoid was blocked by the inhibitors of protein synthesis, cycloheximide and puromycin. However, hydrocortisone showed no effect on the 3H-yohimbine and the 3H-prazosin binding sites. An anti-endocytotic agent, an anti-microtubular agent and protease inhibitors had no effects on the decrease of 3H-clonidine binding sites during culture. These results suggest that the amount of alpha-2 adrenoceptors can change rapidly while alpha-1 adrenoceptors are stable and that glucocorticoids are important in regulation of conformation of alpha-2 adrenoceptor through synthesis of certain protein(s).

Animals↗