Identification of a calcitonin-like diuretic hormone that functions as an intrinsic modulator of the American lobster, Homarus americanus, cardiac neuromuscular system.

In insects, a family of peptides with sequence homology to the vertebrate calcitonins has been implicated in the control of diuresis, a process that includes mixing of the hemolymph. Here, we show that a member of the insect calcitonin-like diuretic hormone (CLDH) family is present in the American lobster, Homarus americanus, serving, at least in part, as a powerful modulator of cardiac output. Specifically, during an ongoing EST project, a transcript encoding a putative H. americanus CLDH precursor was identified; a full-length cDNA was subsequently cloned. In silico analyses of the deduced prepro-hormone predicted the mature structure of the encoded CLDH to be GLDLGLGRGFSGSQAAKHLMGLAAANFAGGPamide (Homam-CLDH), which is identical to a known Tribolium castaneum peptide. RT-PCR tissue profiling suggests that Homam-CLDH is broadly distributed within the lobster nervous system, including the cardiac ganglion (CG), which controls the movement of the neurogenic heart. RT-PCR analysis conducted on pacemaker neuron- and motor neuron-specific cDNAs suggests that the motor neurons are the source of the CLDH message in the CG. Perfusion of Homam-CLDH through the isolated lobster heart produced dose-dependent increases in both contraction frequency and amplitude and a dose-dependent decrease in contraction duration, with threshold concentrations for all parameters in the range 10(-11) to 10(-10) mol l(-1) or less, among the lowest for any peptide on this system. This report is the first documentation of a decapod CLDH, the first demonstration of CLDH bioactivity outside the Insecta, and the first detection of an intrinsic neuropeptide transcript in the crustacean CG.

The effect of nordihydroguaiaretic acid and related lignans on formyltetrahydrofolate synthetase and carboxylesterase.

The lignans nordihydroguaiaretic acid (NDGA), heminordihydroguaiaretic acid (HNDGA) and norisoguaiacin were found to inhibit formyltetrahydrofolate synthetase (formate:tetrahydrofolate ligase (ADP-forming), EC 6.3.4.3) and carboxylesterase (carboxylic-ester hydrolase, EC 3.1.1.1) activity from a wide variety of sources. In all cases, NDGA was the most effective inhibitor. Synthetase activity was reduced by half at NDGA concentrations between 0.11 and 0.24 mM. Esterase activity consisted of NDGA-sensitive and NDGA-resistant forms. The sensitive class was half-inhibited by 2-4 microM NDGA. Irreversible inhibition of formyltetrahydrofolate synthetase by NDGA was observed both at low protein concentration (less than 0.2 mg/ml) and at high protein concentration where precipitation of protein was observed. Inhibition of formyltetrahydrofolate synthetase by NDGA arises from a decrease in Vmax and increase in Km for all substrates. In contrast, NDGA affects only the Vmax parameter of the esterase activity. It is suggested that the broad range of enzymes inhibited by NDGA may be a consequence of the amphipathic character of the molecule and the flexibility to accommodate to a variety of binding sites. It is also suggested that the previously reported ability of NDGA to inhibit phagocytosis may be due to the compound's ability to inhibit carboxylesterases.