Hemeprotein

Monooxygenases owe their catalytic properties to the hemeprotein cytochrome P450 (Fignre 2.3). Within the membrane of the endoplasmic reticulum (microsomal... 

TBTs also cause inhibition of the P450 of monooxygenases. In fish and in the common whelk, TBT causes conversion of P450s to the inactive P420 form (Pent et al. 1998, Mensink 1997). In fish, inactivation was also found with TPT, and was related to the inhibition of ethoxy resorufin deethylase activity (EROD) activity. In these studies, organotin compounds were found both as substrates and deactivators of the hemeprotein (cf. the interaction of organophosphates with B-type esterases). 

Cytochrome P450 A hemeprotein that catalyzes many biological oxidations (see also microsomal monooxygenases). 

Helichrome, an artificial hemeprotein that can hydrolyze aniline, has been reported (Sasaki and Kaiser, 1989). The enzyme is active but significantly weaker than the natural enzyme. 

In general, the NOS isoforms can be grouped into two classes as determined by their expression in cells. Certain NOS isoforms, termed constitutive, appear to be expressed at a fairly constant level in their host cells. However, these isoforms are inactive in their native state and require that the Ca -binding protein calmodulin associate with them in order to generate NO (Schmidt et al., 1991 Busse and Mulsch, 1990 Bredt and Snyder, 1994). Thus NO production by constitutive NOS isoforms is often linked to Ca +-mediated signal transduction cascades that involve soluble guanylate cyclase, which is a hemeprotein that is activated by NO (Arnold et al., 1977). 

Craven, P. A., and DeRubertis, F. R. (1978). Restoration of the responsiveness of purified guanylate cyclase to nitrosoguanidine, nitric oxide, and related activators by heme and hemeproteins Evidence for the involvement of the paramagnetic nitrosyl-heme complex in enzyme activation. J. Biol. Chem. 253, 8433-8443. 

Although, relevant information about ferrous hemeproteins kinetics, dynamics and ligand photodissociation pathways has been obtain, less is known about ferric hemeproteins photophysic processes. Recent studies performed with Hbl-CN and Mb-CN at ultrafast time scale, have suggested that some of the transients intermediaries observed after ferrous complexes ligand photodissociation are observed in ferric Mb and Hbl [7], However, time-resolved infrared data shows that the complex remained six coordinated after photoexcitation. In this work we present ultrafast data on ferric Hbl-NO, HM-N3, HM-H2S and metHbl complexes that suggest a mechanism for the photoinduced reduction of Hbl species. 

Figure 1 shows that after photoexcitation the ferric complexes HM-H2S, Hbl-N3, Hbl-NO and metHbl exhibit an absorption transient formation near -435 nm, which were formed in -300 fs. Time decays varies from 4.5 ps to 6 ps. More than 95 % of signal recovery was observed within 20 ps after photoexcitation. These transients appear to be similar to those observed and assigned to a reduced species of ferrous hemeprotein complexes [6]. An absorption transient formation at 455 nm was also observed and corresponds to formation of the excited states Hbn [3]. As with the ferrous Hbl complexes, the species formed was observed immediately... 

The previous chapter described the types of secondary and tertiary structures that are the bricks-and-mortar of protein architecture. By arranging these fundamental structural elements in different combinations, widely diverse proteins can be constructed that are capable of various specialized functions. This chapter examines the relationship between structure and function for the clinically important globular hemeproteins. Fibrous structural proteins are discussed in Chapter 4. 

Hemeproteins are a group of specialized proteins that contain heme as a tightly bound prosthetic group. Examples of hemeproteins include cytochromes, catalase, hemoglobin, and myoglobin. 

Table 7. EPR g-values of some high-spin hemeproteins...

Table 8. Characteristic spectra of low-spin and high-spin hemeproteins, Fe(III), max (nwi)...

First examples of the amperometric detection of H202 accomplished in such a range were based on the use of an enzyme, namely horseradish peroxidase (HRP), a prototypical hemeprotein peroxidase, which catalyses the reduction of H202 and due to its peculiar structure, allows direct electron transfer between its active site and the electrode surface at low applied potential [14 17]. This approach, although it shows good sensitivity and accuracy, suffers from some important shortcomings such as low stability and the limited binding of HRP to solid surfaces. 

---