Isoform

Most NOS inhibitors are stmcturaHy related to L-arginine and do not differentiate between the isoforms (Table 15). t - / 7-Methy1 arginine (l-NMA) (264) is a competitive inhibitor and also irreversibly inhibits NOS. T.-/ 7-Nitroarginine (l-NNA) (265), L-AP -nitroarginine methyl ester (t.-NAMF) (266),... 

Thyroid hormone receptors (THRs) are subdivided intoa and P types, each having two isoforms. In rat brain, THR, mRNA is present in hippocampus, hypothalmus, cortex, cerebellum, and amygdala. Thyroxine (l-T (284) and triiodothyronine (l-T ) (285) are endogenous ligands for the THRs. TRIAC (286) is a THR antagonist. Selective ligands for PPARs have yet to be identified (Table 16). 

There are two isoforms of COX in animals COX-1 (figure a), which carries out normal, physiological production of prostaglandins, and COX-2 (figure b), which is induced by cytokines, mitogens, and endotoxins in inflammatory cells and is responsible for the production of prostaglandins in inflammation. 

Effect of alteration of heterocyclic nucleus of indolactam V on its isoform selectivity for protein kinase C 95F425. 

Cyclooxygenase is known to exist in two distinct isoforms COX-1 and COX-2 (92JBC21438). The constitutive isoform COX-1 is present in a variety of tissues and is thought to be important in maintaining normal physiological functions such... 

Heterogeneity. Natural aequorin is not a homogeneous protein it is a mixture of many isoforms having isoelectric points ranging from 4.2 to 4.9 (Blinks and Harrer, 1975). The isoform composition may vary to some extent by the purification method employed, due to uneven loss of isoforms during purification. Consequently, the properties of each preparation of aequorin may also vary. By anion-exchange... 

HPLC, about one dozen of the isoforms, aequorins A, B, C, -J, were isolated (Shimomura, 1986a Shimomura et al., 1990). An example of HPLC separation of isoforms is shown in Fig. 4.1.6, and a comparison of the properties of the isoforms is given in Table 4.1.2. 

Table 4.1.2 Properties of the Isoforms of Aequorin (Shimomura, 1986a)... 

Fig. 4.1.14 Relationship between Ca2+ concentration and the initial light intensity of various recombinant semisynthetic aequorins and w-aequorin J (a semisynthetic natural aequorin made from isoform J). The curve number corresponds to the number of semisynthetic aequorin used in Table 4.1.4. A sample aequorin (3 (Ag) was in 3 ml of calcium-buffer solution containing 1 mM total EGTA, 100 mM KC1,1 mM Mg2+ and 1 mM MOPS (pH 7.0), at 23-24°C. From Shimomura etal., 1993a, with permission from Elsevier.

Fig. 9.12 An example of HPLC separation of the isoforms of Mycena citricolor luciferin precursors. The sample adsorbed on a PRP-lcolumn was eluted by a linear increase of acetonitrile from 20% to 40% in a pH 7.5 buffer containing 5 mM tributylamine sulfate. Practically all the peaks have the precursor activity.

Masuda, H., et al. (2003). Chromatography of isoforms of recombinant apoaequorin and method for the preparation of aequorin. Protein Expression and Purification 31 181-187. 

Hanoune J, Defer N (2001) Regulation and role of adenylyl cyclase isoforms. Annu Rev Pharmacol Toxicol 41 145-174... 

The a subunits, for which two isoforms exist in mammals (al, a2), contain conventional protein serine/threonine kinase domains at the N-terminus, with a threonine residue in the activation loop (Thr-172) that must be phosphorylated by upstream kinases (see below) before the kinase is active. The kinase domain is followed by an autoinhibitory domain, whose effect is somehow relieved by interaction with the other subunits. The C-terminal domain of the a subunit is required for the formation of a complex with the C-terminal domain of the (3 subunit, which in turn mediates binding to the y subunit. The al and a2 catalytic subunit isoforms are widely distributed, although a2 is most abundant in muscle and may be absent in cells of the endothelial/hemopoietic lineage. 

AMP-activated Protein Kinase. Table 1 Information about subunit isoforms of AMP-activated protein kinase. Data refer to the full-length forms of the human isoforms. The y2 and y3 isoforms also exist as splice variants that are N-terminal truncations, with lower molecular mass and number of amino acids (38 kDa and 328 amino acids for the short form of y2, 52 kDa and 464 amino acids for the short form of y3). Other splice variants may also exist... 

Isoform Mass (kDa) Gene name Amino acids Domains Domain location (approx.) Domain function Site of major expression Chromosome location... 

NSAIDs inhibit cyclooxygenases (COX), the enzymes that catalyze the transformation of arachidonic acid (a ubiquitous cell component generated from phospholipids) to prostaglandins and thromboxanes. Two isoforms, COX-1 and COX-2, are constitutively expressed in peripheral tissues and in the central nervous... 

---