Low levels of serum 25(OH)D are associated with depressive symptoms, but no effect was found with vitamin D supplementation.

Three isozymes of human tyrosine hydroxylase (hTH1, hTH2 and hTH4) were expressed in Escherichia Cali and purified to homogeneity. Natural catecholamines and related synthetic compounds were found to be potent inhibitors, competitive to the tetrahydrobiopterin cofactor, of all the isozymes. Combining visible spectroscopy and equilibrium-binding studies, it was found that catecholamines bind to hTHZ and hTH2 with a stoichiometry of about 1 .O mol/mol enzyme subunit, interacting with the catalytic iron at the active site. All the isozymes tested were excellent substrates for CAMP-dependent protein kinase ( K , = 5 ~L M , V,,, = 9.5 pmol . min-' . mg kinase-'). The incorporation of about 1 .O mol phosphate/subunit at Ser40 decreased the affinity of dopamine binding by a factor of 10. Conversely, the addition of stoichiometric amounts of Fe(I1) and dopamine to the apoenzymes reduced both the affinity and stoichiometry of phosphorylation by CAMP-dependent protein kinase by 2-3-fold. These data provide evidence for a mutual interaction between the presumed regulatory and catalytic domains of hTH, and show that activation of the enzyme by phosphorylation and inactivation by binding of catecholamines are related events, which probably represent important mechanisms for the regulation of the enzyme activity in vivo.Tyrosine hydroxylase (TH) catalyses the rate-limiting step in the biosynthesis of catecholamines [I], and is regulated in vivo by long-term and short-term mechanisms. The long-term mechanism involves a modulation of TH gene expression[2], while short-term regulation involves activation of the enzyme by phosphorylation [2 -41 and feedback inhibition by catecholamines [5, 61.Human TH (hTH) exists as four different isozyme forms (hTH1-4), generated by alternative splicing of pre-mRNA [7-91. All four isozymes have been detected in the human adrenal medulla [lo], although hTHl and hTH2 seem to be the most abundant species [7-lo]. Three of the isozymes (hTH1, hTH2 and hTH4) have recently been expressed in Escherichia roli as metal-free apoenzymes, and found to be activated by Fe(I1) on binding of 1 Fe/subunit [ll]. Little is known about their regulatory properties in vitro, except that both hTHl and hTH2 are inhibited by catecholamines [12]. This inhibition seems to be partially reversed by phosphorylation [I 21. Furthermore, the isozymes have different phosphorylation sites and may be regulated by different secondmessenger systems [12].

MK-7 taken as Natto over 1 year reduced serum levels of ucOC but did not influence bone loss rates in early menopausal women.