Hirotaka Yamada

Meikai University, Saitama, Saitama, Japan

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Publications (4)8.63 Total impact

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    ABSTRACT: A transient activation of dihydropteridine reductase (DHPR), which is the regenerating enzyme of tetrahydrobiopterin in the system of aromatic amino acid hydroxylases, was studied during the incubation of DHPR with Ca2+-activated protease, m-calpain. The DHPR subunit (29 k) was cleaved by m-calpain just before the 35th (Ser) and 48th (Val) residue from the N-terminus, generating two new fragments of 21 k and 19 k. By determining kinetic parameters, we found that 21 k and 19 k were more active than the native enzyme and that the activation of them was more remarkable and transient against the natural substrate of quinonoid dihydrobiopterin than against a synthesized substrate. Phosphorylation of DHPR by Ca2+/calmodulin-dependent protein kinase II controlled the sensitivity of the enzyme to the Ca2+-activated protease.
    No preview · Article · Jan 2009 · ZOOLOGICAL SCIENCE
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    ABSTRACT: We previously cloned the serum calcium-decreasing factor referred to as caldecrin from pancreas (J. Biol. Chem. 270 (1995) 30315). Caldecrin has been shown to be a chymotrypsin-type serine protease and to inhibit parathyroid hormone or parathyroid hormone-related peptide-induced bone resorption. In the present study, caldecrin was detected in adult rat brain by Western blotting and reverse transcription-polymerase chain reaction analysis. The caldecrin gene was constitutively expressed during postnatal days 1-28 in the brain. By in situ hybridization, the caldecrin mRNA was detected in the whole brain, including the olfactory bulb, cerebrum, hippocampus, thalamus, and cerebellum. These results suggest that caldecrin may play a role in the calcium homeostasis of the central nervous system.
    No preview · Article · Feb 2002 · Neuroscience Letters
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    ABSTRACT: We previously reported on the serum calcium-decreasing activity of recombinant protein factor referred to as caldecrin [Tomomura et al. (1995) J. Biol. Chem. 270, 30315-30321]. To address the mechanism of this serum calcium-decreasing activity, we investigated the effect of rat caldecrin on osteoclastic bone-resorbing activity. Wild-type caldecrin suppressed resorption pit formation by osteoclast on a dentine slice in a dose-dependent manner. The suppressive effect on the bone resorption was not affected by treatment of caldecrin with phenylmethyl sulfonyl fluoride or by use of protease-deficient mutant caldecrins. Recombinant procaldecrin (-13-239), and its fragments (-13-125), (1-111), (1-46), (47-111), and (126-239) were expressed as His-tagged thioredoxin fusion proteins and investigated for their ability to suppress bone resorption. The proform (-13-239) and fragment (-13-125) did not affect the suppressive activity, whereas fragments (1-111) and (126-239) did suppress the bone resorption. The bone-resorbing activity was also suppressed by fragment (47-111), not by fragment (1-46). Overlapping fragments (47-62), (47-79), (47-98), (56-111), (71-111), and (85-111) were compared for their suppressive activity. The fragments (47-62) and (85-111) did not affect the activity, but the other fragments suppressed the bone resorption. A synthetic peptide having the (71-79) sequence suppressed the bone resorption. These results suggest that amino acid sequence corresponding to rat caldecrin (aa 71-79) is responsible for the suppression of bone resorption by caldecrin.
    Preview · Article · Dec 2001 · FEBS Letters
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    ABSTRACT: Sepiapterin reductase (EC; SPR) is an enzyme involved in the biosynthesis of tetrahydrobiopterin; and SPR has been identified as a member of the NADP(H)-preferring short-chain dehydrogenase/reductase (SDR) family based on its catalytic properties for exogenous carbonyl compounds and molecular structure. To examine possible differences in the catalytic sites of SPR for exogenous carbonyl compounds and the native pteridine substrates, we investigated by site-directed mutagenesis the role of the highly conserved Ser-Tyr-Lys triad (Ser and YXXXK motif) in SPR, which was shown to be the catalytic site of SDR-family enzymes. From the analysis of catalytic constants for single- and double-point mutants against the triad, Ser and YXXXK motif, in the SPR molecule, participate in the reduction of the carbonyl group of both pteridine and exogenous carbonyl compounds. The Ser and the Tyr of the triad may co-act in proton transfer and stabilization for the carbonyl group of substrates, as was demonstrated for those in the SDR family. But either the Tyr or the Ser of SPR can function alone for proton transfer to a certain extent and show low activity for both substrates.
    No preview · Article · Feb 2001 · Chemico-Biological Interactions