Properties of clock-controlled and constitutive N-acetyltransferases from chick pineal cells.
Brain Res
; 669(1): 100-6, 1995 Jan 09.
Article
em En
| MEDLINE
| ID: mdl-7712152
ABSTRACT
The pineal gland synthesizes its hormone melatonin (O-methyl-N-acetylserotonin) from serotonin. Acetyl-CoA serotonin N-acetyltransferase (SNAT), the enzyme that catalyzes the committed step in this biosynthesis, is largely restricted to the pineal gland and is regulated by adrenergic and circadian mechanisms. Another enzyme, acetyl-CoA arylamine N-acetyltransferase (ANAT), having an apparently similar activity, is also present in the pineal. This enzyme, however, is not rhythmically regulated. SNAT activity of cultured chick pineal cells was obtained without ANAT after ammonium sulfate precipitation. ANAT activity was retained without SNAT activity after pre-incubation at 37 degrees C. Thus, each enzyme could be examined independently. Overlap in substrate specificity between the two enzymes was minimal. Kinetic analysis of the separated enzyme activities revealed that while SNAT operates via a random or ordered bi bi mechanism, ANAT catalysis occurs through a ping pong bi bi mechanism with substrate inhibition by acetyl-CoA. By size-exclusion chromatography, ANAT was confirmed to be 30-35 kDa, and SNAT was estimated at 15-20 kDa. Taken together, these results indicate that the two enzymes differ in their structure, reactivity, stability, and mechanism of catalysis.
Buscar no Google
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Acetilcoenzima A
/
Glândula Pineal
/
Arilamina N-Acetiltransferase
/
Ritmo Circadiano
Limite:
Animals
Idioma:
En
Revista:
Brain Res
Ano de publicação:
1995
Tipo de documento:
Article